Baby Development 4–6 Months: Milestones, Play & What to Expect

Between 4 and 6 months, your baby transforms from a relatively passive newborn into a curious, engaged, laughing, rolling little person. It is one of the most joyful periods of the first year — and one of the most developmentally rich.

Social and emotional milestones

The social smile (if it hasn't already arrived): A proper, intentional, eyes-and-mouth smile in response to you. Not wind. Not random facial movement. A real smile, meant for you. One of the most memorable moments of the whole first year.

Laughing: First laughs typically arrive around 3–4 months. By 5–6 months, many babies laugh heartily at peekaboo, raspberries, and watching older siblings do silly things.

Recognising familiar faces: Baby clearly distinguishes parents and regular caregivers from strangers. May become slightly wary of unfamiliar faces — this is healthy, normal development.

Responding to your voice: Turns head toward your voice when you speak from out of sight. Clearly knows who mum and dad are by sound.

Expressing emotions: Happy, sad, surprised, confused — a 5-month-old has a surprisingly expressive face and increasingly uses it to communicate.

Physical milestones

Rolling: Many babies roll front-to-back around 3–4 months, and back-to-front around 4–5 months. Some skip one direction entirely. Some roll at 3 months; some not until 6. Wide range is normal.

Hand discovery: Around 3–4 months, babies discover their hands and spend extensive time staring at them. By 5 months, they're reaching deliberately for objects and bringing them to their mouth.

Sitting with support: By 4–5 months, baby can sit in a supported "tripod" position briefly. Full independent sitting typically comes between 6–9 months.

Tummy time progress: A baby who hated tummy time in the early weeks typically accepts and enjoys it more by 4–5 months. By 5–6 months, should be pushing up onto extended arms (the "cobra" position).

Mouthing everything: Everything goes in the mouth — this is how babies explore texture, shape, and temperature at this age. It's developmentally important, not just annoying.

Communication milestones

Cooing and babbling: Rich vocalisations — single consonant-vowel combinations like "ba," "da," "ma." Baby experiments with volume and pitch. "Conversations" where you talk, baby vocalises back, you respond.

Responding to name: By 5–6 months, many babies turn toward their own name. This is an early indicator of language development.

Expressing hunger and tired cues more clearly: By this age, you likely know most of baby's communication signals well. Baby is also getting better at expressing them.

How to support development at 4–6 months

Play ideas

Tummy time with toys: Place interesting objects just within reach during tummy time to motivate lifting and reaching. Mirrors are particularly engaging at this age.

Texture exploration: Different textures — smooth, bumpy, soft, crinkly — stimulate sensory development. Fill a small box with safe tactile objects.

Peekaboo: The classic. Gradually progress from hiding your face to hiding objects under a cloth.

Baby gym: A play mat with hanging toys to bat and grab develops hand-eye coordination and cause-and-effect understanding.

Sitting supported in your lap: Lets baby look around from a different vantage point. Great for book-reading position.

Reading aloud: High-contrast books, books with faces and animals, simple rhyming books. The content matters less than the shared attention and language exposure.

Singing and rhymes: "Row Row Row Your Boat," "Incy Wincy Spider," "Round and Round the Garden." Repetition is the point — familiar songs begin to calm and engage by 5 months.

What baby needs most

• Face time — human faces are the most interesting visual stimulus for babies at this age
• Narration — talk about what you're doing ("I'm changing your nappy now, here comes a wipe, it's a bit cold!")
• Response — when baby vocalises, respond as if it's meaningful conversation
• Floor time — both on their back and on their tummy
• Variety — new environments, new sounds, new faces (within safe relationship framework)

The 4-month sleep regression

Around 3.5–4.5 months, many babies who were sleeping reasonably well suddenly seem to forget how. This is the 4-month sleep regression — a permanent neurological shift in sleep architecture.

Baby now cycles through sleep stages like an adult. If they've been nursing or rocked to sleep, they now can't resettle at the end of each cycle without the same conditions. This is temporary and teachable — babies can absolutely learn to self-settle — but it takes time and consistency.

When to mention development to your health visitor

Speak to your health visitor if, by 6 months:

• Baby isn't smiling at familiar faces
• Doesn't seem to track moving objects with eyes
• Doesn't turn toward sounds
• Legs feel very stiff or very floppy
• Not bringing hands to mouth
• No interest in people or faces

Developmental milestones are a range, not a deadline. But if something feels off, always mention it — early support makes an enormous difference.

Capture it all in TinyYears

This is one of the most milestone-dense periods of the first year — first roll, first laugh, first time sitting up. Log each one with the date and a video clip in TinyYears. You'll treasure the record.