Every single person has a skeleton made up of many bones. These bones give your body structure, let you move in many ways, protect your internal organs, and more.
It's time to look at all your bones — the adult human body has 206 of them!
and in baby's the bones differ here is the explanation:
When you were a baby, you had tiny hands, tiny feet, and tiny everything! Slowly, as you grew older, everything became a bit bigger, including your bones.
A baby's body has about 300 bones at birth. These eventually fuse (grow together) to form the 206 bones that adults have. Some of a baby's bones are made entirely of a special material called cartilage (say: KAR-tel-ij). Other bones in a baby are partly made of cartilage. This cartilage is soft and flexible. During childhood, as you are growing, the cartilage grows and is slowly replaced by bone, with help from calcium.
By the time you are about 25, this process will be complete. After this happens, there can be no more growth — the bones are as big as they will ever be. All of these bones make up a skeleton that is both very strong and very light.