Chapter four focuses on body growth, brain development, and influences on physical growth. During the time, a child goes from an infant to a toddler they grow uncontrollably. By the time an infant is six months they have doubled from their birthweight. Instead of growing steady overtime infants experience times where they do not grow at all and times where they grow a lot over a day. The child body begins to proportion and different parts of the body grow at different rates. Infants also begin to experience brain development. Neurons store and transfer information in the brain and it is between 100 and 200 billion presents in the brain. The development of neurons impacts how other parts of the brain develops. Chapter four also focus on how