Let me explain. Babies have more bones than adults because as they grow up, some of the bones fuse together to form one bone. This is because babies have more cartilage than bone. New born babies have around 305 bones. A baby's skeleton is mostly made up of cartilage. As a person grows up, most of this cartilage turns into bone in a process called ossification. By adulthood, the skeleton has just 206 bones.