Baby development 3 to 9 months: growth phases

Between 3 and 9 months, watching your baby reach new baby development milestones is truly thrilling. During this period of baby growth from 3 to 9 months, your little one will develop in two connected but different ways: physical growth spurts - sudden increases in weight and length - and developmental milestones, such as sitting, babbling, and grasping. Both are exciting to witness, and sometimes exhausting. In this article, we’ll guide you through what to expect at each stage.

What is a growth spurt in babies?

A growth spurt is a short period of rapid physical growth during which your baby gains weight and length more quickly than usual. Baby growth spurts are distinct from developmental leaps, which involve new skills and behaviours rather than physical size changes.

Common signs of a growth spurt include:

• Feeding more frequently (cluster feeding)

• More fussiness or irritability than usual

• Sleeping more - or sleeping less and waking more at night

• Seeming hungrier than usual, even after a full feed

Growth spurts don’t follow a strict timetable. Every baby is different, and timing can vary by several weeks. During baby growth from 3 to 9 months, common growth spurt windows include:

• Around 3 months

• Around 6 months

• Around 9 months

These are approximate, not fixed. You can track your baby’s growth with our Baby Growth Chart Calculator to monitor their progress.

What can my baby do at 4 months?

Your baby is growing rapidly, and changes will come thick and fast - physical, emotional, and cognitive. Around 3–4 months is a common time for a growth spurt, so your baby may seem hungrier or fussier than usual before a burst of new development. Your baby is now interacting more with the world, learning from it and you, their favourite playmate.

By four months, your baby probably:

• Holds up their head on their forearms or even their hands. Holds their head steady while being held in a seated position, all the better to have a talk with you.

• Can spot you across the room and follow you with their eyes as you move around.

• Knows how to get your attention by crying, dropping something or even emitting a fake ‘cough’.

• Bats at objects and sometimes manages to reach and grab things. If your baby grabs something, they’ll shake it or stick it in their mouth. If they let go, it’s an accident that surprises them.

• Finds their own hands very interesting. They’ll swipe at them, touch them and just look at them.

• Dribbles a great deal, making their toys and you very wet, but their teeth probably aren’t coming through yet.

• Recognises your voice and will calm down for at least a little while if you call to them from another room. Your baby is learning to anticipate and wait.

• Can fall asleep on their own if you start a sleeping ritual and give them a small toy or blanket to comfort them.

Tracking these baby development milestones is a wonderful way to celebrate your baby’s unique baby development stages - explore more with the Baby Development Milestones tool.

What can my baby do at 6 months?

By six months, your baby is sitting up or getting ready to sit up, and their back is straightening out. This is a new perspective for your baby, and they enjoy it!

At six months, your baby probably:

• Laughs out loud, smiles, and squeals.

• Will ‘tease’ you by dropping and throwing things and making noise to get your reaction. They’re also experimenting with ideas of space and disappearance.

• May pull to stand up on furniture or in their cot.

• Can pass things from one hand to the other.

• Puts almost everything into their mouth.

• Babbles to you as if in conversation.

• Has a first tooth, or several teeth.

• Turns towards sound.

• Can comfort themselves with a thumb, dummy, or a rolling activity.

• Rolls over both ways.

• Begins to be wary of strangers as they’re getting cleverer at working out who’s familiar and who’s new in their world.

Around 6 months is another common growth spurt window, often coinciding with the introduction of solid foods. Your baby may seem hungrier than usual or feed more frequently during baby growth from 3 to 9 months - this is perfectly normal.

Just when you think you have it all under control, your baby will decide to challenge you again - by starting to move! You’ll have to begin thinking about safety in these terms. As your baby begins eating their first solid foods, you’ll need to be aware of choking hazards as well. These are all healthy baby development milestones and exciting baby development stages to celebrate.

What can my baby do at 9 months?

Your baby is on the move: exploring, investigating, and experimenting. They love hiding things and playing peek-a-boo because now they understand object permanence - that things still exist even when out of sight. You’ll need to be on duty constantly - to reassure your baby of your love and, just as importantly, to keep them safe. This is the age when many parents realise how strong their baby’s personality really is and how much they want to be a part of and into everything.

At nine months, your baby probably:

• Sits pretty well without support and can twist and turn from a stable sitting position.

• Can play with toys while sitting.

• Can move forward in some way, whether creeping, crawling, or shuffling. Some babies never crawl but still manage to move around somehow.

• Pulls themselves up to stand, and sometimes gets stuck. (Soon they’ll learn to plop down again.)

• Has a pincer grasp - the index finger and thumb work together to pick up small objects - and uses it. (You can be sure they will find every little thing that has fallen into the carpet or rolled under a table.)

• Uses their index finger to poke at things, such as switches, buttons, and electrical sockets.

• Wants you in view at all times. They’ll go back and forth to check in as they play. Your baby may experience separation anxiety in babies, getting very anxious when you’re out of sight. Your baby may greet strangers and even people they know with wary looks, if not blood-curdling screams. Keep in mind that they’re not being rude - they’re just very aware of the difference between their family and close caregivers and those who are less familiar.

• Babbles in a good imitation of talking. You’ll even start to hear ‘mama’ and ‘dada’ once in a while. Your beaming response to these words will let your baby know that they’re special.

• Knows their own name, turns when you call them, recognises some words, and is very interested in people talking around them.

• Has their first teeth, usually the bottom and top incisors.

• Wakes up and is difficult again at night. That’s because these days they miss people and all the fun they’ve had during the day.

• Is no longer happy just to be held and cuddled. Now they’ll want to get involved with everything around them.

• Is ready to take control of their feeding. Finger foods and a cup are very interesting at this stage, especially because they have mastered the pincer grasp.

• Makes noise and trouble in new ways by throwing, banging, shaking, and taking apart their toys. Having Mum or Dad there to retrieve these items only adds to the fun!

Around 9 months is another common growth spurt period. Your baby may feed more, wake more at night, and seem clingier - all of which is perfectly normal during baby growth from 3 to 9 months. These baby development milestones and baby development stages show just how far your little one has come.

Is it a growth spurt or could my baby be unwell?

It’s natural to feel unsure whether your baby’s fussiness is a growth spurt or something more concerning - the signs can look surprisingly similar.

Typical growth spurt signs:

• Feeding more frequently than usual

• Fussiness or irritability that passes within a few days

• Changes in sleep - sleeping more, or waking more at night

• Seeming unsettled but otherwise well and responsive

Signs that may indicate illness:

• High temperature (38°C or above in babies under 3 months; 39°C or above in babies 3–6 months)

• Persistent crying that sounds different from their usual cry, or a high-pitched cry

• Appearing floppy, drowsy, or difficult to rouse

• Refusing feeds repeatedly or unable to keep fluids down

• Fewer wet nappies than usual (a sign of dehydration)

• Pale, blotchy, blue, or grey skin

Baby growth spurts typically last 2–3 days and then settle. If you’re ever unsure, trust your instincts and contact your GP or health visitor.

When should I contact my GP or health visitor?

You know your baby better than anyone. If something feels wrong, always trust your instincts.

Contact your GP or health visitor if your baby:

• Has a temperature of 38°C or above and is under 3 months old

• Has a temperature of 39°C or above and is between 3 and 6 months old

• Is not feeding normally and you’re worried

• Is crying constantly and cannot be consoled, or the cry sounds unusual

• Is unusually drowsy or difficult to wake

• Has fewer wet nappies than usual

Call NHS 111 if:

• It is evening or the weekend and your GP surgery is closed

• You are concerned but do not think it is an emergency

Call 999 or go to A&E if your baby:

• Stops breathing

• Has a purple-red rash that does not fade when a glass is pressed against it (possible sign of sepsis)

• Will not wake up

For non-urgent questions about your baby’s baby development milestones and baby development stages, your health visitor is an excellent first point of contact.