The skeleton of an infant is comprised of 300 bones. As a child's body grows, many of the bones in the skeleton fuse together until he is left with the 206 bones found in an adult skeleton.
An infant's skeleton contains more cartilage than bone. During the growth of a child, most of the cartilage found in the skeleton begins to turn into bone through a process known as ossification. Other bones fuse together in to form larger bones that have the greater strength and durability that are necessary to support the heavier weight of a fully grown adult body.