As a child grows, the bones fuse, or grow together, and the cartilage present in a child's body turns into bone because of calcium. Babies are born with 300 bones in their bodies and by the time they reach adulthood, they have 206 bones.
By the time a person reaches the age of 25, the bone fusion process is complete. At this age, growth has completely stopped and the bones will be as large as they will ever be.
Bones are important because they help a person move, support muscle tissue and protect the internal organs. Bones in the human body are always changing and are made up of the outer surface called the periosteum, compact bone and bone marrow.