Step-by-step explanation:
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. Ossification is the the process of creating bone, that is of transforming cartilage (or fibrous tissue) into bone. As the child grows, these soft areas ossify into actual bone. The knee cap, for example, begins to ossify between ages 3 and 6.