How many bones are in an 8-year-old child?

Approximately 250. Some of the 300 bones a person is born with (such as the individual plates that make up the skull, and those at the base of the spine) have already fused together, while several others (like the multiple small bones in each wrist and ankle) won't finish doing so until around puberty.

At the end of adolescence, the last of the growth plates in the arms and legs will have fused and stopped growing, leaving the average adult with around 206 bones.