A newborn baby has about 270 bones. Interestingly, newborns have more cartilage than bones in their bodies. Cartilage provides the flexibility and softness to the body, so that infants are able to pass through the birth canal easily. With time, the bones fuse together to provide more rigidity to the human body and we end up with stronger and larger bones. This fusion is more prominent in our skull and spine and it reduces the number of bones in an adult human being to 206 bones. A strong skeleton is required to protect vital organs, gives rigidity to the limbs (thereby enabling them to apply force) and provides the body with a definite shape.
The cartilage is slowly replaced by a calcified bone matrix through a process called endochondral ossification and causes formation of hardened bone tissue.
A newborn baby has about 300+- bones. These soft bones and cartilage will fuse together to form the 206 bones an adult human has.