Childhood bone development. X-ray of a 4-year-old child's feet, showing how the bones of a child's foot are still developing and are relatively flexible until ossification occurs to make the foot more rigid. The bones seen here are those of the ankle, heel and mid-foot, while the longer bones towards the end of the feet are the metatarsal bones and the phalanges of the feet (the toe bones). At lower left and lower right are the ends of the lower leg bones, the fibula and tibia.