Developmental Milestones [Part 1: Infancy]

Published: 13 Jan 2022

Developmental Milestones [Introduction]


In this exciting stage things happen extremely quickly. We stare in wonder as this miracle unfurls before our eyes - and it all starts with our child’s brain.

The brain

When a baby is born, it’s brain is around 25% of its fully matured adult weight. By age 2, it will be 80%. That’s some extraordinary growth! The connections between their 100 billion or so brain cells multiply at an incredible rate from around 2.5 trillion connections at birth to as many as 15 trillion connections at age two. These connections develop as a baby takes in information from its environment. Each new piece of information affects the structure of the brain and the connections between their neurons (brain cells).

At birth, our children’s subcortical structures are the most mature. (The cortex is the outer part of the brain we see in movies - the bit with all the squiggly intestine-looking stuff. So anything subcortical is underneath that cortex.) The brain develops from bottom to top and from rear to front. So areas related to vision, hearing, breathing, feeling, body temperature regulation, and reflexes are much more neurologically developed at birth and through the first year of life than those related to cognition, emotion regulation, and even things like balance and coordination. Those latter functions are more likely to be located in the cortex, which is still developing. 


At birth our babies already have a number of reflexes that are ready to go:

Moro Reflex : AKA the startle reflex. A loud noise or sudden jolt makes the infant stretch its arms to the side and then hug them back to the chest with clenched fists.

Sucking Reflex:  gently touch your baby’s lips or tongue and she begins to suck.

Rooting Reflex: gently stroke the corner of your baby’s mouth and he turns his head and tongue, trying to locate a nipple to feed from.

Grasping Reflex: Maybe my favourite. When you put your little finger into the palm of your infant’s hand and she grasps you and holds on tight.

These reflexes are uncontrollable. But they’re important for your child to survive.


Crying is another reflex that is important to an infant’s survival. They tend to cry when: 

  • they are uncomfortable (needing food or a nappy change, or when the temperature is too cold or hot), 
  • when they are mad (usually when they can’t feed or are tired because they’ve been woken up), or 
  • when they are in pain.

There are cross-cultural differences in the way parents respond to an infant crying. A 1979 study found that parents in African hunter-gatherer cultures responded faster to a crying infant than parents in our culture. The average interval between a baby’s cry and a parent picking up that child was 6 seconds for hunter-gatherers and 3.83 minutes for middle-class American mothers. (And no, it’s not just because the house was bigger or the stereo was on.) Research shows that responsiveness is associated with optimal development in our children. 

This stuff matters. We’ve discovered that when we are responsive to our children, they develop secure attachments to us. Those attachments impact on their wellbeing, development, and relationships throughout life. 

Physical growth

Physical growth happens fast during infancy too. A healthily developing child will grow from about 3kgs at birth to about 6kgs by four months,and then a little over double that again to about 13-14kgs by age two, which is about one fifth of their healthy adult weight. Babies gain about 2.5cm each month in length/height for the first year, and by their second birthday your baby will be about half his adult height. 


Babies can’t see very well. The muscles that control their eyes are not developed and your baby may not be able to track you as you walk across the room. In fact, her eyes might even look in different directions from time to time! Anything more than 20cms from your baby’s face will be blurry, but that’s just about perfect because as you breastfeed your baby, she’ll be looking 20cms up, straight into your face. It’s almost like it was meant to be! 

By about four months of age eyesight is rapidly improving and by eight months, your child develops depth perception, just in time to avoid crawling over the edge of the balcony (because it’s at this point that kids become particularly mobile). By age one, vision is essentially developed fully.

Milestones in infancy (summary)

Physical and motor skill

  • 6 weeks: no longer need you to hold their neck all the time to support their head. This ability is fully developed by about four months.
  • 5 months: Can roll from stomach to side or back.
  • 8 months: Can pull herself to a standing position (and is usually sitting up with some gentle support).
  • 12 months: Can walk a short distance unaided.
  • Fine motor skills for reaching and grasping begin developing around 3 months, and by 9 months your baby can pick up small items between thumb and forefinger.

Sensation and perception

  • Birth: Hearing, touch, taste and smell are well developed from the beginning.
  • Vision develops fast over first four months and baby can track moving objects, perceive colours, and move eyes with intention to see specific things.
  • 5 months: Can identify faces.
  • 8 months: development of depth perception (for safety). Understands size constancy (so large things that are distant seem small but child knows they’re not). Vision at adult capability or thereabouts.


  • Birth: Baby knows how to show she’s upset.
  • 4 months: Laugh in response to mild surprise (peak-a-boo).
  • 6 months: Shows anger, shyness and surprise.
  • 6-12 months: Fear is shown, particularly for strangers.
  • 2 years: begins to understand embarrassment and also pride. 


  • Enormous growth in capacity to understand complex ideas due to development of attention in early months.
  • Piaget’s “Sensorimotor Stage” highlights that from 4 months to 8 months children can develop control over things.
  • 8-12 months: children begin to understand object permanence (hidden objects), and will search for something in the last place they saw it.

Social development

  • 2 months: Smiling (and not from gas).
  • 4 months: is friendly towards people, and not fussed about who gives the cuddles.
  • 7-12 months: attachment hierarchy forms and separation anxiety becomes a reality.

What you can do for your infant

During the first 6 months, focus on lots of physical contact and high levels of responsiveness. Try the following: 

  • Speak in ‘motherese’ (high pitched, sing-song voice), 
  • Serve and return in speaking so they feel you are engaged, 
  • Play games like peek-a-boo, 
  • Read stories, 
  • Sing songs,
  • Be in their space as much as is practical 

In addition, copy their sounds. Laugh a lot. Avoid looking at your phone when feeding. Instead, look at them. Let them meet your eyes and study your face. Talk to them lots. 

Other ideas could include using a pram that allows your baby to face you while you push , read them simple stories or picture books, lay on the floor with them, and just enjoy soaking up their perfect innocence. 

As your child grows, teach basic turn-taking skills. Use descriptive words like “see the big brown cow” or “look at the little white dog” or “that’s a round red ball”. From about the age of one, give your child paper and crayons. Let them tear and colour and explore. The more tactile, the better! Talk all the time. Describe what your child is doing or what you are doing. Make it detailed. The more words they hear, the better. And did I mention reading? Keep reading! And from a little over 12 months (or younger) sing counting songs like 1, 2, 3, 4, 5. Once I caught a fish alive. These behaviours help the development of neural circuitry in the language and speech areas of the brain, and help them develop a rich understanding of their environment. 

Finally, in the last 6-9 months of infancy, use words to describe emotions, ask questions of your child, encourage pretend play (so a plastic block could be a steering wheel), build with blocks, kick and throw balls, name everything around you like household items, body parts, animals and nature. 

Most important of all - be there. Be their safe haven, their secure base. Be the person who tries to greet them with a smile and pure delight. Help them feel safe and secure.

All of these things aid your child’s development by providing their brain with the perfect stimulation for healthy growth, strong neural connections that facilitate security, and the reassurance that they are loved. 

Developmental Milestones [Part 2: Toddlers]




Your Growth Guide






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