Four Months Old: Personality Is Starting to Show

By four months, you're no longer caring for a newborn — you have a baby with opinions, preferences, and what can only be described as a sense of humor. The difference from those first bleary weeks is striking, and it keeps getting better from here.

Social & emotional development

Your four-month-old has discovered something powerful: they can use their charm to get your attention. That smile isn't just a reflex anymore — it's deliberate, deployed to reel you in. You might also catch the beginnings of a laugh, more of a breathy chuckle than a full giggle, when you do something they find amusing.

Smiles intentionally to get attentionChuckles when you try to make them laughUses sounds, movement, or eye contact to engage you

Language & communication

The vowel sounds are arriving — soft, round coos of "ooh" and "aah" that your baby produces with clear satisfaction. Better still, they're becoming conversational about it. Talk to your baby and pause; they'll often fill the silence with a sound of their own. They've also figured out which direction your voice comes from and will turn toward it.

Coos with vowel sounds ("ooh", "aah")Responds vocally when spoken toTurns head toward familiar voice

Thinking & learning

Early cause-and-effect reasoning is taking root. When your hungry baby spots the breast or bottle, they open their mouth in anticipation — a small but meaningful sign that they're connecting events and outcomes. They're also becoming fascinated by their own hands, staring at them with a focused intensity that's genuinely amusing to watch.

Anticipation

Opens mouth at the sight of breast or bottle when hungry

Self-discovery

Studies their own hands with real curiosity and concentration

Movement & physical skills

Motor development this month is all about gaining control over the body. Head stability is a big one — your baby can now hold their head up steadily when you're holding them upright. During tummy time, they push up onto their forearms and look around with growing confidence. Hands are increasingly useful too: reaching, swinging at objects, grasping what's placed in them, and making the well-worn journey back to the mouth.

Steady head control when held uprightGrasps a toy placed in their handSwings arm toward dangling objectsBrings hands to mouthPushes up on forearms during tummy time

How to support your baby this month

Four months is a wonderful age for play. Your baby is alert, engaged, and ready to interact. These are some of the best things you can do together.

• Keep up the vocal back-and-forth. When your baby makes a sound, mirror it back and wait. They'll respond. This is the earliest form of conversation.

• Set up a safe play area on the floor with a few toys within reach. Let your baby kick, swat, and explore without being confined to a bouncer or swing.

• Let your baby mouth safe objects — it's one of the primary ways they gather information about the world right now. Just make sure items are large enough not to pose a choking risk.

• Hold a bright toy in front of your baby and move it slowly side to side, then up and down. Watch their eyes track it — visual tracking is a skill actively developing this month.

• Sing, narrate, and read aloud daily. The language doesn't need to be simplified — your baby benefits from hearing the full range of your vocabulary.

• Play peek-a-boo. It seems simple, but it introduces the concept that things continue to exist even when hidden — a foundational idea in cognitive development.

• Avoid extended time in bouncers, swings, or car seats outside of travel. Your baby needs floor time to build the strength and coordination that's coming next.

• Stick with breast milk or formula only. Solid foods, water, and other drinks aren't needed or appropriate until around six months.

Dental expectations at four months

Four months is right on the edge of when teething can begin — so this is a good time to get informed and prepared. Some babies will cut their first tooth this month; many won't see one for several more months. Both timelines are completely normal.

Teething may be starting — or just ahead

Most babies get their first tooth between 4 and 7 months, with the lower central incisors (the two front bottom teeth) typically leading the way. Signs that teething is beginning include increased drooling, fussiness, swollen gums, and a strong urge to chew on anything within reach. A low-grade temperature can occur, but a true fever is not a symptom of teething — contact your pediatrician if your baby's temperature rises noticeably.

Hands to mouth = teething prep (and normal development)

Your four-month-old is bringing their hands to their mouth constantly — this is a normal developmental behavior and also provides natural gum relief if teeth are on their way. Offering a clean, chilled (not frozen) teething ring can help. Avoid teething gels containing benzocaine, which are not recommended for babies under two.

Keep up gum care — and add a toothbrush to your shopping list

Continue wiping your baby's gums after feeds with a damp cloth. Now is also a good time to pick up a soft-bristled infant toothbrush so you're ready the moment that first tooth appears. When it does, brush twice daily using a smear of fluoride toothpaste — about the size of a grain of rice.

Mention it at the 4-month checkup

Your baby's four-month well-child visit is an ideal opportunity to bring up any teething signs you've noticed and ask your pediatrician about fluoride supplementation — especially if your household water supply isn't fluoridated. They can also confirm when to schedule that first dental appointment.

Reminder: the first dental visit is recommended by your baby's first birthday, or within six months of the first tooth — whichever comes first. If teething is starting now, that appointment may be sooner than you think.

Milestones are guideposts, not deadlines. If your baby hasn't hit one or more, or seems to have lost a skill, bring it up with your pediatrician. Early support makes a genuine difference.