Is it true that a baby's bones are not fully formed?

Yes, many of its bones are still in the forms of cartilage, a flexible, gristly tissue, such as that which makes up your nose, ear, and part of your ribs.

Everybody's bony framework (that is the skeleton) starts out as cartilage and hardens gradually. Even a baby's skull bones are soft and not yet joined together. By the time a child is twelve, the bones are hard and fully formed although still growing in length.