top of page
Child Brain Development
Child Brain Development
Child Brain Development
Child Brain Development


1 year

3 year

5 year

Child Brain Development

7 year

Child Brain Development
Child Brain Development

10 year



Early Brain Growth and Development

An amazing transformation takes place during the first 5 years of life.  With so much to learn before they start school, this is a memorable time and a life changing period of essential development.  

An abundance of learning is accompanied by a huge spurt in brain growth. At birth, a baby’s brain is about one-quarter the volume of an adult brain. The rest of a newborn’s tiny body is not even close to one-quarter of their adult size. Children’s brains continue to grow rapidly.


By 3 years of age, a child’s brain is already more than 80 percent of adult size. By 5 years of age, it’s grown to about 90 percent of adult size. Children’s large brain size is why their heads are so big for their bodies. Over time, the rest of the body slowly grows and catches up with the brain and head.

Within the brain, and extending throughout the body is a network of cells called neurons. Neurons are the building blocks of the brain. Working together, they form a complex signaling network. You can think of your brain and all of its neurons like your body’s communications team. 

Neurons the building blocks of the brain

Neurons may be the building blocks of the brain, but no neuron works alone. Instead, neurons connect up with each other — like wires — into neural circuits and work together to accomplish certain tasks. Depending on how complex the task, some circuits contain only a few neurons, while others contain millions.

Early Child Brain Development

Interactive Influences and Experience Shape the Developing Brain

During this process early experiences literally shape the construction of the developing brain.  Genes provide a blueprint for when the brain circuits are developed, the timing of different circuitry, but how those circuits are actually formed is shaped by the environments and experiences in which children are growing.

When asked the question of: what do we mean by the environment? What do we mean by  experience? What scientists have learned from decades of research in humans and in animals as well is the interactions that young children have with the important adults in their lives that really constitute the essence of the impact of the environment on their development.

This is a time of critical opportunity for adults and children to become mutually interactive. We call this the serve and return nature of interaction between very young children, beginning at birth, and the adults and care givers who care for them.

Parents close and engaging interations with their child

Adults closely observe how a baby is feeling, what a baby is doing, and including you know as children get older, a child makes a sound or says something, the adult responds, an  adult does something, makes a facial  expression, engages the child, responds.

It's that back-and-forth serve and return, mutual interaction, that is literally shaping the circuitry of the brain. Biologically, the brain is expecting responsive, stable, predictable  interactions, and when it doesn't have that kind of responsive environment can result in important neural pathways from forming, or fading away from lack of stimulation. Research also shows that babies feel distress when their attempts to connect with a parent or caregiver are persistently ignored.

It also includes other important adults in a child's life: extended family, neighbors, friends, staff in early childhood programs, teachers, coaches. All of these individuals and the nature of their relationships with children, how responsive it is, how interactive it is, literally creates the environment in which brain architecture is developed for better or for worse.


When child development researchers examine and talk about Early Childhood Development, they often break it down into different categories: cognitive development, language development, social development, emotional development. 


The biology of the development of the brain tells us that the brain is a highly integrated organ,  and although there are areas of specialization for these different developmental functions, the circuitry that underlies these skills is exquisitely interrelated, so you can't  separate these different functions in the brain.


They're highly inter-connected. Promoting healthy development in young children, if our primary interest is in their social development, emotional well-being, language, or cognition, or how they think, all of those different functions must be nurtured and strengthened at the same time due to the brain working in concert with these domains.  

Early Child Brain Development

Core Principles of How the Brain Develops Early in Life

The brain is built over time, and it's built from the bottom up. In the beginning, simple early experiences affect and shape the development of simple circuits for simple skills. As time passes  and as children have the capacity for more complex behavior, the brain builds more complex circuits.

In the early stages, simple experiences affect and shape the development of simple circuits for simple skills. And as time goes on and as children have the capacity for more complex  behavior, the brain builds more complex circuits on top of a foundation of simple circuits, and this circuitry, which ultimately involves trillions of connections, is built very rapidly in the early years. 

Baby brain connections

In the first few years of life, more than 1 million new neural connections form every second. These connections are called synapses.

Early Child Brain Development

Building Brain Circuitry and its Influences

Based on being exposed to their exciting new world with new sounds of talking talking adults, children around them, the brain starts to differentiate the distinctions among sounds that may sound similar. This is its sensitive period, which means it is optimally responsive to  environmental input. 

It's the time when the brains circuits are being formed. However, when that sensitive period of circuit formation  ends, that part of the brain is less responsive to environmental influences. The circuit is formed, the circuit is stabilized, the circuit is finished, and now the brain goes on to the next level of circuits. One of the principles of this biological process is when a circuit is being  made, that's the time you can most affect its formation for good or for bad.

Once it has been stabilized, you cannot go back and rewire this stage. If you didn't get it right or it wasn't done properly, the higher-level circuits have to make accommodations. If the circuit was made well and it's sturdy and then it's stabilized, that's the foundation that you have for the rest of your life for that particular function.

This notion of critical and sensitive periods is very important in Early Childhood Development because it means these are the times for particular parts of the brain that the brain is optimally
plastic, it’s optimally flexible and most responsive to environmental input. This is the period  when we want to make sure that the environment of relationships, the resources available to families, the care  provided by people other than parents, is providing the kind of responsive serve and return interaction that the brain is expecting and needs.

As growth continues it goes on to build more complex circuits and it loses a lot of its plasticity on these simpler circuits. It becomes more difficult to change later and why timing is  important. Similary, timing matters for different parts of the brain at different times, and that's exactly why, when we missed the early childhood period and we begin to think about how to provide schooling for children who don't have a strong foundation in learning.


We can make things better, but after this growth stage is missed it becomes much more costly  later, through intervention for example, to meet similar early stage growth. During this intervention to gain and develop this lost period, we have to work harder, and the outcome is not as good as we would have had as a result of some of the circuits that we need as a foundation have already been built and stabilized.

The Crucial Brain Foods all Children Need

The first 1,000 days of life are crucial for brain development — and food plays an important role. The ways that the brain develops during pregnancy and during the first two years of life are like scaffolding: they literally define how the brain will work for the rest of a person’s life....Learn more from Harvard Health and Dr. Claire McCarthy at Harvard Medical School.



Center on the Developing Child, Harvard University

Jack P. Shonkoff, M.D., is the Julius B. Richmond FAMRI Professor of Child Health and Development at the Harvard T.H. Chan School of Public Health and the Harvard Graduate School of Education; Professor of Pediatrics at Harvard Medical School and Boston Children's Hospital; and Director of the university-wide Center on the Developing Child at Harvard University. He currently serves as chair of the National Scientific Council on the Developing Child.

Institute for Learning & Brain Sciences

bottom of page