All of this learning is accompanied by a huge spurt of 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. If it were, the average newborn in North America would weigh about 40 pounds! Children’s brains continue to grow, and quickly. 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. If our bodies grew at this same pace, the average American would be over 5 feet tall by the age of 5. 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.

Inside 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.