Can you please explain why bone cancer is so common in children?

Actually is is rare: The number of children diagnosed with cancer per year is approximately 125 per million children aged 0-15 years. The 2 most common bone cancers, osteosarcoma and ewing sarcoma, account for 5% of that number, or approximately 6.3 of those cancer types per 1 million children.

It isn't common: Primary malignancies of bone are very rare in children, adolescents and adults. There are only 450 cases/year of osteosarcoma in the us in children and a little less ewing sarcoma. That is compared to about 200, 000 cases /year of breast cancer. That being said bone and soft tissue sarcomas make up about the 4th or 5th most common cancer in children though still exceedingly rare.

It isn't.: Bone and joint cancers only represent 0.2% of all new cancers diagnosed in the US. 28% of cases occur in patients under 20, most commonly in teenagers, not young children.