Skip to main content

Brain Development Stages In Children


At birth, an infant’s brain includes roughly 86 billion brain cells (neurons), which is nearly the entire number of neurons that the human brain will ever have 2.

A baby’s neurons have roughly 50 trillion synapses, but an adult brain has about 500 trillion.

At the age of two, an adult’s synapse density is half that of a toddler.

Even though it is only 25% the size of an adult, a baby has nearly the same number of neurons as an adult.

The number of synaptic connections has expanded to 1000 trillion by the age of three.

A child’s brain volume has reached 90% completion by the age of five and a half.

Early Developmental Milestones

Here are some brain development stages to look out for in your child’s life:

In the third week following conception, neurons begin to develop in the fetal brain.

From birth, the auditory system develops, so they start to recognize voices and sounds in their environment.

Over the course of the first five weeks, babies start to learn and strengthen their memory and emotional awareness as it relates to other people. That happens in the amygdala and hyphothalamus.3.  They watch facial expressions intently. This is when babies start to register emotion and connection. They begin to feel relationship experiences that cause them pain, such as separation, rejection, or crisis, as well as starting to understand what will bring them the feelings of comfort, soothing and being held.  This is when expectations start to form.

At 9 months, they have developed large motor skills and start to roll over and sit up.  Their brains also learn how to engage in games like peek-a-boo.  At this stage they start to realize that when mom or dad isn’t there and realize that they miss them. This may be the beginning of some separation anxiety around you leaving. At this stage they are learning through being tactile, including putting things in their mouth.  It’s a new way to explore and take in information.

At the age of one year a baby’s brain has more than doubled in weight. Many children are learning to speak around this age. Fine motor skills emerge, and patterns are starting to form well-paved pathways in the brain.  The 5 senses also become more finely tuned so bright colors are noticed more, tastes and smell evolve, and they are becoming more aware of the ability to move their body.

At what stage does the brain stop developing?

You may be wondering, when is the brain truly developed? On average, the brain stops developing around the age of 25.  The prefrontal cortex is the last portion of the brain to reach full development. The prefrontal cortex is where complex behaviors such as executive functioning and impulse control are developed. And yes, this isn’t full developed until the mid-20’s.  That is why underage drinking, drugs and concussions are of great concern to many. 5

We’ve talked about the brain development stages, but it’s worth noting that the brain really never stops evolving. The formation and alteration of interconnections in our brain is a continual process that continues throughout our lives. The good news is that neural pathways are formed and changed all the time, as we develop new habits and learn new things. However, the bad news is that as we grow older, the neural path formation and change progress at a much slower rate.6

The Brain Depends on Experience

One of the most noticeable elements of human brain development stages is synaptic pruning. The network of synapses rapidly increases during the first year of life and continues to do so into toddlerhood.  Think about the fact that everything is new to them.  They have a lot of information to process on a daily basis.  They don’t need to remember every little detail of everything that they encounter.  Only those details or experiences that are either repeated or impactful to them are the synapses that will be retained.

The stimulation of certain neurons, the development of new connections between neurons, and the strengthening of existing connections are all part of the myelination process. Unused synaptic connections will eventually be deleted during synaptic pruning 6.  Synaptic pruning sounds intense, but it is a neurological mechanism that removes redundant neurons and synapses to increase neuronal transmission efficiency. After synaptic development, this process occurs between early childhood and puberty. It is basically the brain decluttering what information has been stored but is not being used.

Life experiences literally mold the brain, which is why interacting with your child, instead of putting them in front of a screen all the time is so important. Babies can adapt to any environment they are born into, which is great news for parents as we all struggle with how to meet the needs of our kids and keep up with all of the information available out there to help us. 7. The most important thing that you can do for your child is to be there for them and be present with them.

Critical Periods and Plasticity

The first few years of a child’s life are the most critical and sensitive to long term brain development. It is impossible to overestimate the importance of developmental timing and connection to parents or caregivers in early life.  During this critical period, synaptic connections in specific brain regions become more fluid and malleable. Connections are formed or strengthened as the child has new experiences. As kids grow up, the synapses become more fixed and less flexible. The “ruts” in the roadmap of the brain have been paved in.

For example, learning new languages is much easier for young children. They have a better probability of mastering a non-native language before puberty. With this understanding we can see that the time from infancy through adolescence is important for language development. Communicating (verbally and non-verbally), reading, and writing is key at this stage and it’s also why kids learn technology so easily and adapt to new situations so quickly.  Sensory Play is also incredibly important as they learn more and more how to BE in their bodies.

Nature vs. nurture in the case of brain development

There was a fascinating study done in rats with genetic predispositions of being fearful and easily stressed.  When these baby rats were left with their biological mothers, of the same genetic makeup, they tended to in fact be fearful and easily stressed.  When the researchers placed the baby rats with “foster” mothers who were not of the same genetic makeup of being fearful, the baby rats did not grow up to be fearful or easily stressed.

There was a Dutch researcher by the name of Dymphana Van den Boom who took this a step further with mothers who had babies who tended to be temperamentally reactive.  She wanted to see if the mothers could learn to respond to their babies to help calm their stress.  She designed short term instruction and support for them to help them learn ways to calm their babies and the mothers were able to better respond to them.  These children did, in fact, grow up with strong and secure attachments.

In the age-old nature-versus-nurture debate, nurture (i.e. Connection) wins.

Final Thoughts on Brain Development

Neuroplasticity and experiential stimuli are two important building blocks in the foundation of a child’s brain development stages. While we don’t have to be perfect parents, good enough parenting can be extremely beneficial to a child in the short term, but it also impacts so many areas of their entire life. What does good enough parenting look like?  Show up, be present, connect with your child.  Let them know that they are safe, seen, and heard.  Those small things make a monumental difference to the quality of their childhood and overall life of your child.


1. Azevedo FAC, Carvalho LRB, Grinberg LT, et al. Equal numbers of neuronal and nonneuronal cells make the human brain an isometrically scaled-up primate brain. J Comp Neurol. Published online April 10, 2009:532-541. doi:10.1002/cne.21974

2. Graham J. Children and Brain Development: What We Know About How Children Learn. Cooperative Extension Publications.

3. Sue Gerhardt Why Love Matters, how affection shapes a baby’s brain. Routledge Pub;2015: 52,60,87

4. Lebel C, Walker L, Leemans A, Phillips L, Beaulieu C. Microstructural maturation of the human brain from childhood to adulthood. NeuroImage. Published online April 2008:1044-1055. doi:10.1016/j.neuroimage.2007.12.053

5.Fuster, J. M. (2001, May 1). The prefrontal cortex—an update. Neuron, 30(2), 319-333. Retrieved from

5. McMahon E, Wintermark P, Lahav A. Auditory brain development in premature infants: the importance of early experience. Annals of the New York Academy of Sciences. Published online April 2012:17-24. doi:10.1111/j.1749-6632.2012.06445.x

6. Tau GZ, Peterson BS. Normal Development of Brain Circuits. Neuropsychopharmacol. Published online September 30, 2009:147-168. doi:10.1038/npp.2009.115

7. Huttenlocher P. Synapse elimination and plasticity in developing human cerebral cortex. Am J Ment Defic. 1984;88(5):488-496.

8. Stiles J, Jernigan TL. The Basics of Brain Development. Neuropsychol Rev. Published online November 3, 2010:327-348. doi:10.1007/s11065-010-9148-4

9. Balbernie R. Circuits and circumstances: the neurobiological consequences of early relationship experiences and how they shape later behaviour. Journal of Child Psychotherapy. Published online January 2001:237-255. doi:10.1080/00754170110087531

10. Hair NL, Hanson JL, Wolfe BL, Pollak SD. Association of Child Poverty, Brain Development, and Academic Achievement. JAMA Pediatr. Published online September 1, 2015:822. doi:10.1001/jamapediatrics.2015.1475

(c)2022, I Shine Brite
All rights reserved
Terms of Use: No portion of this document may be replicated, reproduced or edited without the express written consent of Jenny Warner or I Shine Brite.
No claim to copyright is made for original U.S. Government Works.



Leave a Reply