Children in early childhood are physically growing at a rapid pace. If you want to have fun with a child at the beginning of the period, ask them to take their left hand and use it to go over their head to touch their right ear. They cannot do it. Their body proportions are such that they are still built very much like an infant with a very large head and short appendages. By the time the child is five years old though, their arms will have stretched, and their head is becoming smaller in proportion to the rest of their growing bodies. They can accomplish the task easily because of these physical changes.