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The first year · 4 to 5 months

4 to 5 Months: Development, Research, and What Helps

Last reviewed · 17 min read · 12 activities · 12 common questions · 85 sources · Plain-text version

Around 4 months, babies start reaching for the world and putting all of it in their mouths. Here's what's developing, what research says about sleep training, early solids, and teething, and what actually helps.

A smiling parent walks down a neighborhood sidewalk carrying a delighted baby in a front carrier.

At a glance

  • Most 4-month-olds chuckle, coo back at you, hold a toy you hand them, and push up on their forearms. Rolling and real laughs usually come by 6 months.
  • Mouthing is how babies explore. Keep anything small enough to choke on, plus button batteries and magnets, out of reach.
  • Solids usually start around 6 months, not before 4. Skip cereal in the bottle: it's a choking risk and didn't improve sleep in a trial.
  • Sleep training is a family choice, not a requirement. Trials found it can improve sleep and parents' mood, with no harm found years later.
  • Stop swaddling once your baby tries to roll. Always lay them down on their back; if they roll both ways on their own, you can leave them.
  • Teething often starts between 4 and 7 months. Skip numbing gels, homeopathic tablets, and amber necklaces; a firm rubber teether works.
  • US vaccine guidance shifted in 2026. Ask your pediatrician which schedule they follow at the 4-month visit.

Your 4-to-5-month checklist

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Around 4 months, babies start reaching for the world, and then putting it in their mouths. This guide covers 4 to 5 months. For the month before, see the 3-month guide; first foods are covered in the 5-month and 6-month guides.

What's developing

A baby lying on a rug turns toward the camera, working on rolling over.

CDC's milestone checklists list skills that at least 75% of babies show by each age, so a missed milestone is a reason to check in, not to wait and see (Zubler et al., 2022).

Milestones by 4 months

By 4 months, most babies (CDC):

  • Social: smile on their own to get your attention, chuckle (not yet a full laugh) when you try to make them laugh, and look at you, move, or make sounds to get or keep your attention.
  • Communication: coo ("oooo," "aahh"), make sounds back when you talk to them, and turn their head toward your voice.
  • Thinking: open their mouth when they're hungry and see the breast or bottle, and look at their hands with interest.
  • Movement: hold their head steady when you hold them, hold a toy you put in their hand, swing an arm at toys, bring their hands to their mouth, and push up onto their elbows or forearms on their tummy.

Coming by 6 months: laughing, taking turns making sounds, blowing raspberries, reaching for a toy they want, rolling from tummy to back, and pushing up on straight arms (CDC). Born early? Use corrected age (age in weeks minus the weeks born early) until age 2 (AAP).

Rolling and pushing up

Rocking on the tummy, kicking, and "swimming" with the arms usually appear at about 5 months and lead to rolling. Most babies roll tummy to back first (the reverse is normal too), and many roll both ways by 7 months (AAP). The AAP's safe sleep guidance notes that rolling often begins around 3 to 4 months and can start earlier (Moon, AAP), which changes swaddling and where you leave your baby (see safety).

Hands, grabbing, and mouthing

By 4 months, most babies can easily bring objects to their mouth. Next comes a mitten-like raking grip; passing toys hand to hand comes at 6 to 8 months, and the pincer grasp at about 9 months (AAP). Babies now spot nearby objects and often reach for them (AAP). Mouthing is part of how they learn (CDC).

Chuckles, coos, and babble

Chuckles come first; a full laugh is a 6-month milestone (CDC). Babbling often starts around 4 months, with the rise and fall of your language, so it can sound like a question or a statement (AAP).

Cause and effect

Around 4 months, babies start figuring out that they can make things happen: a kick shakes the crib, a wave rattles the rattle. Sometime after 4 months, they also begin to learn that things still exist when they're out of sight (AAP).

Eyes

At 4 months, babies see colors and shades better and may love circles and spirals, one reason faces are so appealing. Wandering or crossing eyes should be going away by 2 to 3 months (AAP).

Sleep at 4 to 5 months

Babies 4 to 12 months need 12 to 16 hours of sleep in 24 hours, naps included (Paruthi et al., 2016); the AAP supports that guidance (AAP). Regular sleep cycles arrive at about 4 months (AAP), but "sleeping through the night" varies a lot (see common questions).

Growth and feeding

Many babies double their birth weight at about 4 months (AAP). Breast milk or formula is still the only food and drink your baby needs; CDC says babies aren't ready for other foods, water, or other drinks for about the first 6 months (CDC).

Drool and first teeth

Teething typically starts somewhere between 4 and 7 months, usually with the two front teeth, top or bottom. Timing varies a lot and may run in families (AAP). Drool alone isn't a reliable sign a tooth is coming (see the research below).

What the research says

Some of these findings are solid. Two famous ones are still argued about.

1. Young babies remember. In a classic experiment, 3-month-olds learned that kicking moved a crib mobile. They usually forgot after about 8 days, but a brief reminder the day before the test let them remember for 2 to 4 weeks (Rovee-Collier et al., 1980). Takeaway: Repeated games and routines stick. Your baby is learning what to expect.

2. Taking turns shapes babble. In a study of 40 three-month-olds, babies whose adult partner answered in a back-and-forth rhythm made more speech-like sounds than babies whose partner responded at random times (Bloom et al., 1987). Takeaway: When your baby makes a sound, answer, then pause.

3. Babies know their name before they show it. In a lab, 4½-month-olds preferred listening to their own name over other names, even names with the same rhythm (Mandel et al., 1995). Looking when you call their name doesn't show up on CDC's checklist until 9 months (CDC). Takeaway: Use your baby's name often. They're taking it in long before they turn to it.

4. Object permanence at 5 months is contested. In the famous "drawbridge" study, 5-month-olds looked longer at a screen that seemed to rotate through a hidden box, which researchers read as surprise, a sign babies knew the hidden box was still there (Baillargeon et al., 1985). A 1999 study found babies looked longer at the bigger rotation even with no box at all, suggesting they may simply like more motion (Rivera et al., 1999). Takeaway: What young babies "know" is hard to measure. Play peekaboo for the fun of it.

5. "Sticky mittens" haven't held up well. In a 2002 study of 32 three-month-olds, babies who played in Velcro mittens that let them "pick up" toys later explored objects more (Needham et al., 2002). A pre-registered trial of 96 Swedish 3-month-olds found daily mitten training didn't improve reaching (van den Berg et al., 2022), and a review rated the overall evidence low to very low (Righetto Greco et al., 2023). Takeaway: No special gear needed. Floor time and toys within reach do the job.

6. Sleep training can help, and no lasting harm has been found. A review of 52 studies found that behavioral methods, from letting a baby settle alone to gradual approaches and bedtime routines, reliably improved sleep (Mindell et al., 2006). In an Australian trial of 328 mothers of 7-month-olds with sleep problems, those taught these methods reported fewer sleep problems and less depression at 12 months (Hiscock et al., 2007); at age 6, the 225 children followed up showed no differences in emotions, behavior, stress, or closeness to parents (Price et al., 2012). A trial of 43 babies 6 to 16 months old found no rise in stress hormones and no effect on attachment (Gradisar et al., 2016). One small study of 25 babies raised a concern: they stopped crying at bedtime by day 3, but their stress hormones stayed high (Middlemiss et al., 2012). Takeaway: It's a choice, not a requirement. These trials involved babies 6 months and older.

7. Early solids barely change sleep. In a trial of 106 babies, rice cereal in a bedtime bottle didn't help them sleep through the night (Macknin et al., 1989). In a UK trial of 1,303 breastfed babies, those assigned to start solids at 3 months slept about 16.6 minutes longer a night and woke slightly less often at 6 months than those who waited (Perkin et al., 2018). Meanwhile, in a US study of 847 children, formula-fed babies who started solids before 4 months had about 6 times the odds of obesity at age 3, a link that doesn't prove cause (Huh et al., 2011). Takeaway: Guidance still says around 6 months, not before 4. Ask your pediatrician.

8. Teething symptoms are mild and brief. Parents of 125 babies logged symptoms daily from 4 months to age 1. Drooling, fussiness, and a slight temperature rise clustered in the 8 days around each new tooth, and fevers over 102°F weren't linked to teething (Macknin et al., 2000). A meta-analysis of 16 studies agreed that any temperature rise didn't amount to a fever (Massignan et al., 2016). Takeaway: A high fever or a very sick-seeming baby isn't "just teething." Call.

Parenting techniques

Talk, pause, and copy

When your baby babbles, gestures, or cries and you respond with eye contact, words, or a hug, those exchanges help build brain circuits (Harvard Center on the Developing Child). When your baby lands on a sound, repeat it back, then say simple words that contain it (AAP).

Script: "Bah? Bah! Ball. Bottle. Baa, baa, black sheep." (Pause.) "Your turn."

Floor time beats container time

WHO advises floor play several times a day, including at least 30 minutes of tummy time spread through the day, and not keeping babies strapped into strollers, high chairs, or carriers for more than 1 hour at a time (WHO). CDC suggests daily play on a mat or blanket and not keeping babies in swings, strollers, or bouncy seats for too long (CDC). Put toys in a circle around your baby so reaching builds the muscles for rolling and crawling (AAP).

Make mouthing safe, not off-limits

Let your baby mouth safe things that aren't sharp, hot, or small enough to choke on (CDC). Federal rules ban small parts in toys meant for children under 3, using a test cylinder sized like a young child's throat (CPSC), but household items aren't tested. Keep toys that can be squeezed to fit in a mouth, button batteries, and coin batteries away from your baby, and check under cushions for coins and other small things (Bradin, AAP). Many choking incidents start with an older sibling sharing a toy or snack, so teach them the rule too.

A bedtime routine you can repeat

A survey of more than 10,000 mothers linked consistent bedtime routines with better sleep, though it can't prove cause (Mindell et al., 2015), and a trial in older babies found a routine helped within weeks (see Brush, book, bed). Keep it short and the same each night, and don't put your baby to bed with a bottle (AAP).

Calm with less, one step at a time

For a fed, changed, rested baby who's still fussy, the AAP suggests adding comfort one step at a time: your eyes, then your voice, then a hand on their chest, and only then picking up, rocking, or a pacifier. Give each step a few minutes; piling everything on at once can overload them (Ideran & Fishbein, AAP).

If you're thinking about sleep training

Sleep training is optional. If night waking is wearing you down:

  • Start with the basics. Calm, quiet night feeds; lively days; and putting your baby down drowsy so they practice falling asleep in their own bed (AAP).
  • Know your options. Gradual methods wait a little longer each night before going in to soothe; "cold turkey" means checking but not soothing. Pediatricians generally give the okay at 3 or 4 months, so talk it over first (Lurie Children's).
  • Keep safe sleep non-negotiable. Back to sleep, a bare crib, and room-sharing for at least the first 6 months, whatever method you use (Moon, AAP).
  • Respond when something's wrong. Hunger, a dirty diaper, or illness always gets an answer (AAP).

Watch for solids readiness, but wait

CDC says babies can start solids at about 6 months and that starting before 4 months isn't recommended (CDC); WHO guidance also starts other foods at about 6 months (WHO, 2023). For readiness signs, see Is my 4-month-old ready for baby food? One thing to plan for now: if your baby has severe eczema or an egg allergy, guidelines suggest introducing peanut as early as 4 to 6 months, after checking with your pediatrician (NIAID). The how-to is in the 5-month and 6-month guides.

Soothing sore gums safely

Rub your baby's gums with a clean finger, or offer a firm rubber teething ring that isn't frozen (AAP). Skip numbing gels, homeopathic tablets, and amber necklaces; the FDA warns they can cause serious harm (FDA). See What can I give my baby for teething pain? for more.

Work with your baby's temperament

Some babies are easygoing; others are intense or slow to warm up. Cuddling, talking, and distraction can calm an intense baby. A quiet, sensitive baby needs extra time to warm up and people who approach slowly, and may need your attention more than they show (AAP).

Script for a visiting relative: "She warms up slowly. Talk to her from over here for a few minutes before you pick her up."

Look after yourself, too

The AAP recommends that pediatricians screen for postpartum depression at the 4-month visit (Earls et al., 2019). Partners count: in a meta-analysis, about 10% of fathers had depression around a birth, rising to about 26% at 3 to 6 months after birth (Paulson & Bazemore, 2010); a larger, later one of 74 studies found about 8% and no effect of timing (Cameron et al., 2016). Help now: call or text 1-833-TLC-MAMA (1-833-852-6262) or 988; in an emergency, call 911 (CDC).

What to teach

No lessons yet. Your baby is learning a lot from everyday life, though:

  • I can make things happen. Rattles rattle, kicks shake the mat, and smiles bring you closer (AAP).
  • Conversations take turns. Copy your baby's sounds and see how long you can keep it going (CDC).
  • That's my name. Say it often (CDC).
  • Days have a rhythm. Steady sleep and feeding routines help (CDC).

Screens: video chat only

CDC recommends limiting screens to video calls with loved ones; screen time isn't recommended before age 2 (CDC). The AAP says babies under 18 months learn best from real-world interactions (Munzer, AAP) and calls video chat with faraway family fine (Hill, AAP).

Family life is the curriculum

Chores and responsibility start around age 1; the 1-year guide covers that. For now, let your baby watch and listen while you cook, fold laundry, or water plants, and narrate what you're doing. It's talk time for them and real work for you.

Activities to try

Every activity here is for an awake, alert baby with an adult right there. Stop when your baby looks away, fusses, or arches. If they get sleepy, lay them on their back in their own sleep space (Moon, AAP).

How we rate the evidence
Strong evidence
Randomized trials or systematic reviews show a consistent benefit.
Moderate evidence
Consistent observational research, or a major guideline (AAP, WHO) built on research.
Emerging evidence
Small or early studies. Plausible, not yet proven.
Mixed evidence
Studies disagree, or reviews rate the evidence as weak.

Too tired to choose? Let us pick one.

  1. Toy circle tummy time

    Moderate evidence
    Time
    5 to 10 minutes, several times a day
    Builds
    Neck, shoulder, and core strength; reaching; rolling
    1. Lay your baby tummy-down on a firm mat on the floor.
    2. Place 3 or 4 toys in a circle around them, some just out of reach (AAP).
    3. Get down at eye level and cheer each reach and pivot.

    Make it work: Short sessions add up. Lying on your chest counts too.

    Evidence: Moderate. A systematic review of 16 mostly observational studies linked tummy time to better gross motor development and to rolling and crawling (Hewitt et al., 2020); WHO recommends at least 30 minutes a day spread out (WHO).

  2. Roll-over helper

    Emerging evidence
    Time
    2 to 5 minutes
    Builds
    Rolling, body awareness
    1. With your baby on their back on the floor, hold a toy off to one side, just above their shoulder.
    2. As they twist toward it, let them try first, then gently help their hip follow through.
    3. Celebrate the roll, then try the other side.

    Make it work: Do this on the floor only, never on a bed or couch.

    Evidence: Emerging. Rolling both ways typically comes between 4 and 7 months (AAP); no studies show that practice makes it happen sooner.

  3. Toy hand-offs

    Emerging evidence
    Time
    A few minutes, a few times a day
    Builds
    Grip, reaching, hand-eye coordination
    1. Offer a light rattle or soft ring by touching it to your baby's palm.
    2. Let them grab, shake, and mouth it.
    3. Offer the next toy to the other hand.

    Evidence: Emerging. Holding a toy you put in their hand is a 4-month milestone, and CDC suggests easy-to-grip toys like rattles and cloth books (CDC); the activity itself hasn't been studied.

  4. Kick and see

    Emerging evidence
    Time
    2 to 5 minutes
    Builds
    Cause and effect, leg strength
    1. With your baby on their back on the floor, hold a crinkly toy or a soft drum where their feet can reach it.
    2. When they kick it and it makes a sound, react with delight.
    3. Hold it still and see if they kick again.

    Make it work: Never tie anything to your baby's arms or legs.

    Evidence: Emerging. In lab studies, 3-month-olds learned that kicking made a mobile move and remembered it for days (Rovee-Collier et al., 1980), and the AAP describes babies this age discovering that kicks shake things (AAP). Home versions haven't been tested.

  5. Sound copycat

    Emerging evidence
    Time
    2 to 5 minutes, during calm, alert times
    Builds
    Turn-taking, speech-like sounds
    1. Wait for your baby to make a sound.
    2. Copy it back, with a smile.
    3. Pause, and count how many turns you can keep going.

    Evidence: Emerging. In a study of 40 three-month-olds, adults who answered in turn got more speech-like sounds back (Bloom et al., 1987); CDC suggests copying your baby's sounds (CDC).

  6. The name game

    Emerging evidence
    Time
    A minute, any time
    Builds
    Name recognition, attention
    1. From one side, softly say your baby's name in a sing-song voice.
    2. When they look or still, smile and say, "That's you!"
    3. Try from the other side.

    Evidence: Emerging. Babies 4½ months old recognized the sound of their own name in a lab study (Mandel et al., 1995), and CDC suggests using your baby's name often (CDC).

  7. Board book time

    Moderate evidence
    Time
    5 minutes, once or twice a day
    Builds
    Language, attention, closeness
    1. Choose a board or cloth book with bright pictures or faces.
    2. Let your baby hold, pat, and mouth it.
    3. Point and name things in a lively voice; follow what grabs their attention.

    Make it work: It doesn't matter what you read. The time together is what counts (AAP).

    Evidence: Moderate. The AAP recommends shared reading starting at birth, based on research linking it to language, literacy, and social-emotional development (Klass et al., 2024).

  8. Peekaboo

    Emerging evidence
    Time
    A few minutes
    Builds
    Anticipation, social play, early ideas about hidden things
    1. Cover your face with your hands or a cloth.
    2. Pop out with "Peekaboo!" and a big smile.
    3. Watch for smiles or chuckles, and keep going while they're having fun.

    Evidence: Emerging. CDC suggests playing peekaboo with 4-month-olds (CDC), and the AAP says hiding games help babies learn that things still exist out of sight (AAP); what babies understand at this age is debated (Rivera et al., 1999).

  9. A parent and a baby in a carrier smile at their reflection in a tall mirror.

    Mirror smiles

    Emerging evidence
    Time
    2 to 3 minutes
    Builds
    Attention, social interest
    1. Hold your baby facing an unbreakable mirror, or prop one beside them during tummy time.
    2. Point and say, "There's [name]! There's me!"
    3. Make faces and watch them watch you.

    Evidence: Emerging. Liking to look at themselves in a mirror is a 6-month milestone (CDC), and the AAP lists an unbreakable mirror among toys for 4-month-olds (AAP); mirror play hasn't been tested as an activity.

  10. Lap bounce songs

    Emerging evidence
    Time
    A song or two
    Builds
    Leg strength, rhythm, laughter
    1. Sit with your baby facing you, feet on your thighs.
    2. Hold them securely under the arms and let them push and bounce.
    3. Sing a rhyme and pause before the last line for a big finish.

    Make it work: Keep it gentle and always support their head and trunk.

    Evidence: Emerging. CDC suggests holding your baby under the arms with their feet on your lap and letting them bounce (CDC); not studied as an activity.

  11. A safe mouthing basket

    Emerging evidence
    Time
    5 minutes of floor play
    Builds
    Exploring with hands and mouth, grip
    1. Fill a shallow basket with 3 or 4 safe objects of different textures: a firm rubber teether, a soft cloth book, a wooden spoon, a big plastic cup.
    2. Let your baby pick, shake, and mouth.
    3. Swap one item a day to keep it new.

    Make it work: Nothing small enough to fit in their mouth, nothing with batteries, strings, or loose parts.

    Evidence: Emerging. CDC says letting babies mouth safe things is how they learn (CDC), and the AAP suggests spoons and unbreakable cups as cheap toys (AAP); the basket itself hasn't been studied, but choking rules are firm (Bradin, AAP).

  12. Brush, book, bed

    Moderate evidence
    Time
    10 to 15 minutes at the same time each night
    Builds
    Predictable sleep cues, early oral care, reading
    1. Wipe your baby's gums with a soft, damp cloth (or brush a first tooth with a rice-grain smear of fluoride toothpaste).
    2. Read one short book in dim light.
    3. Lay your baby on their back in their own sleep space at a regular time.

    Evidence: Moderate. In a trial of 405 families of babies and toddlers, a consistent bedtime routine improved sleep and mothers' mood within weeks (Mindell et al., 2009); the AAP recommends this routine (AAP).

Common questions

When do babies start rolling over?

Many babies start rolling between 4 and 6 months, usually tummy to back first. Rolling from tummy to back is on CDC's 6-month list (CDC), and many babies roll both ways by about 7 months (AAP). The AAP's safe sleep guidance notes that rolling often begins around 3 to 4 months and can start earlier (Moon, AAP). Daily tummy time helps (Hewitt et al., 2020). Stop swaddling at the first signs of rolling (AAP).

Is my 4-month-old ready for baby food?

Probably not yet: CDC says babies can start solids at about 6 months, and starting before 4 months isn't recommended (CDC). Readiness signs include sitting up with support, steady head control, opening the mouth when food comes, and swallowing rather than pushing food out. Every baby is different, so talk it over at the 4-month visit. If your baby has severe eczema or an egg allergy, ask about peanut now (NIAID). See the 6-month guide for first foods.

Should I put rice cereal in my baby's bottle?

No, not unless your pediatrician recommends it. The AAP says cereal in a bottle can cause choking and too much weight gain, though a doctor may suggest it for reflux (AAP). It also doesn't seem to help sleep: in a trial of 106 babies, bedtime cereal in the bottle didn't change how many slept through the night (Macknin et al., 1989). When you do start cereals, CDC suggests a variety of fortified cereals, since feeding only rice cereal can increase arsenic exposure (CDC).

Is it normal for my 4-month-old to wake up more at night?

Yes, night waking at this age is common and normal, whether or not you call it a "4-month sleep regression." Babies don't have regular sleep cycles until about 4 months (AAP), and sleep develops unevenly: in a study of 75 New Zealand babies, 21 still weren't sleeping from 10 p.m. to 6 a.m. at 12 months (Henderson et al., 2010). In a Canadian study of 388 babies, 27.9% to 57.0% of 6- and 12-month-olds didn't sleep 6 to 8 hours straight, and that wasn't linked to their development (Pennestri et al., 2018). Call your pediatrician if your baby seems sick, has a fever, or is feeding poorly.

Is sleep training safe for babies?

Trials so far haven't found lasting harm. They found behavioral sleep methods improved sleep and parents' mood (Mindell et al., 2006; Hiscock et al., 2007), with no differences in emotions, behavior, stress, or parent-child closeness at age 6 (Price et al., 2012) and no effect on attachment a year later (Gradisar et al., 2016). Most of those babies were 6 months or older. It's still a family choice, not something every baby needs. Talk to your pediatrician about timing, and keep every safe sleep rule in place.

How much should a 4-month-old sleep?

About 12 to 16 hours in 24 hours, including naps, is recommended for babies 4 to 12 months old (Paruthi et al., 2016; WHO). Some babies need a bit more or less. A regular wake time, active days, and a short, predictable bedtime routine help (AAP).

Is my 4-month-old teething, or just drooling?

It could be either, since teething often starts between 4 and 7 months (AAP), but drool alone doesn't prove a tooth is coming. In a study of 125 babies, drooling, gum rubbing, and fussiness were linked to teething only in the few days around each tooth's arrival, no symptom showed up in more than 35% of teething babies, and no set of symptoms reliably predicted a new tooth (Macknin et al., 2000). Swollen, tender gums are the most common sign (AAP; Massignan et al., 2016). Teething doesn't cause a true fever, so a rectal temperature of 100.4°F (38°C) or higher, or a very unhappy baby, needs a call to your pediatrician (AAP).

What can I give my baby for teething pain?

Start with a clean finger rubbed on the gums or a firm rubber teething ring that isn't frozen (AAP). Don't use benzocaine or lidocaine gels, which can cause serious harm, or homeopathic teething tablets (FDA). Ask your pediatrician before any pain medicine; ibuprofen isn't for babies under 6 months unless a doctor says so (AAP).

Are amber teething necklaces safe?

No. The FDA has received reports of deaths and serious injuries, including strangulation and choking, from teething jewelry like amber necklaces (FDA). The AAP says they don't relieve pain at all, and that nothing should ever go around a baby's neck (AAP).

Are baby walkers and activity centers safe?

Baby walkers with wheels aren't safe; the AAP has called for a ban on them. Babies in walkers can roll down stairs, reach hot liquids, and move more than 3 feet in a second, and walkers don't help babies learn to walk. Stationary activity centers without wheels are a safer alternative (AAP). Even so, WHO advises not keeping babies strapped into seats for more than 1 hour at a time (WHO), and floor play is better for building strength.

Does my breastfed 4-month-old need iron or vitamin D?

Breastfed babies need vitamin D drops, and the AAP also recommends iron for breastfed babies, though its advice on when to start iron has shifted, so ask your pediatrician about timing and dose. The AAP recommends breastfed babies get 400 IU of vitamin D a day, and formula-fed babies need a supplement until they drink about 32 ounces of formula a day (Porto & Abu-Alreesh, AAP). The AAP's 4-month checkup page recommends a liquid iron supplement of 1 mg per kilogram a day for breastfed babies until iron-rich foods start at about 6 months (AAP), while its July 2026 clinical report calls for iron supplements for exclusively breastfed babies by 6 months (AAP, 2026).

What vaccines does my baby get at 4 months?

Under the AAP schedule, your baby may get second doses of the rotavirus, DTaP (diphtheria, tetanus, and whooping cough), Hib, pneumococcal (PCV), and polio (IPV) vaccines at 4 months (AAP). For the 2026-2027 season, it also recommends RSV protection for babies under 8 months entering their first RSV season, unless they're protected by an RSV vaccine given during pregnancy (AAP). US guidance has been changing: the AAP and CDC schedules have differed in 2026 (AAP), a court stalled many federal vaccine policy changes and the government appealed (STAT, 2026), and in October 2026 the AAP's immunization schedule editor said the federal vaccine advisory committee wasn't meeting (Contemporary Pediatrics, 2026). Ask your pediatrician which schedule they follow.

Safety and when to call your pediatrician

Safe sleep for a baby who rolls

Every rule in the newborn guide still applies: on the back for every sleep, a firm, flat surface with only a fitted sheet, and room-sharing (never bed-sharing) for at least the first 6 months. Once your baby rolls both ways on their own, you don't need to keep turning them onto their back, as long as the crib is bare (Moon, AAP). Stop swaddling at the first signs of rolling; a sleep sack that lets your baby move freely is fine (AAP). Never use weighted sleep sacks, swaddles, or blankets (Moon, AAP).

Falls happen fast now

Never leave your baby alone on a changing table, even for a moment, even strapped in (AAP), or alone on a bed or couch, since they may be rolling soon, if not already (AAP). Use bouncers on the floor only, never on a counter, table, or soft surface, and stop using one when your baby can sit up alone (CPSC). Any head injury in a baby under 1 needs a call to the doctor right away (AAP).

Small objects, batteries, and cords

  • Button and coin batteries stuck in the throat can burn through it within 2 hours. If you think your baby swallowed one, go to the ER or call 911 right away. Tape battery covers shut and save the National Battery Ingestion Hotline, 800-498-8666 (AAP).
  • Magnets swallowed (or suspected) mean go to the ER now (AAP).
  • Poison: call Poison Help at 1-800-222-1222 (AAP).
  • Cords: use cordless blinds or keep cords out of reach (AAP).

Burns

Grabbing hands reach mugs. Don't carry your baby and a hot drink or soup at the same time, and set your water heater so the faucet runs no hotter than 120°F (AAP).

Car seats

Rear-facing in the back seat as long as possible, up to the seat's rear-facing limits; outgrowing the infant seat means a convertible seat, still rear-facing. Straps go at or below the shoulders, snug enough that you can't pinch slack, with the chest clip at armpit level and no bulky coat underneath (AAP).

Sun

The AAP says babies under 6 months should be kept out of direct and indirect sun because of the risk of heat stroke; use shade, light long sleeves, and a wide-brimmed hat, and avoid outings from 10 a.m. to 4 p.m. (Gupta & Mahoney, AAP).

Fever at 4 to 5 months

A rectal temperature of 100.4°F (38°C) or higher is a fever. For babies 3 to 6 months, the AAP advises contacting your pediatrician within 24 hours about any fever, sooner for 104°F (40°C) or higher or a baby who seems very sick (AAP). Don't use ear thermometers before 6 months (AAP).

Call 911 if your baby

  • Is struggling for each breath, has stopped breathing, or has bluish lips or face (AAP)
  • Choked on a small object that could still be stuck (AAP)
  • Can't be woken up, isn't moving, or is very weak (AAP)
  • Has a seizure after a head injury (AAP)
  • Has purple or blood-colored spots on the skin with a fever (AAP)

Go to the ER now if your baby

  • Has any trouble breathing, or ribs pulling in with each breath (AAP)
  • Has a bulging soft spot, is hard to wake, or isn't alert when awake (AAP)
  • Vomits green (bile) or blood (AAP)
  • Swallowed, or might have swallowed, a button battery or magnet (AAP)

Call your pediatrician right away if your baby

  • Has a fever of 104°F (40°C) or higher, cries nonstop, or cries when touched or moved (AAP)
  • Has signs of dehydration: no wet diaper in more than 8 hours, a very dry mouth, or no tears (AAP)
  • Had any head injury, including a fall from a bed, couch, or changing table (AAP)
  • Swallowed a small object but seems fine (AAP)
  • Looks or acts very sick, or you think they need to be seen urgently (AAP)

Don't wait on development worries

CDC's advice: you know your child best, so talk with your pediatrician and ask about developmental screening if your baby isn't meeting milestones, has lost skills, or you have other concerns (CDC). You can also call your state's early intervention program for a free evaluation; you don't need a referral or a diagnosis (CDC). Bring it up if your baby:

  • Doesn't smile on their own or chuckle when you play
  • Doesn't coo, make sounds back to you, or turn toward your voice (CDC)
  • Doesn't hold their head steady when held, or push up on their forearms on their tummy
  • Doesn't bring their hands to their mouth or hold a toy you give them
  • Has eyes that still cross or wander (AAP)
  • Has lost skills they used to have

The 4-month checkup

Expect weight and length checks, a full exam, questions about sleep, feeding, and safety, a check-in on how you're feeling, and possibly an anemia screen if your baby was born early or small (AAP). Bring questions about iron, vitamin D, solids, and teething. For vaccines, see What vaccines does my baby get at 4 months?

Sources

This guide is general education that summarizes published research and guidance from groups like the American Academy of Pediatrics, the CDC, and the WHO. It isn’t medical advice, and every child develops on their own timeline. Your pediatrician knows your child; if something feels wrong, call them. In an emergency, call 911.

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