Final answer:
Growth of bone in childhood originates from the epiphyseal plate, which is responsible for lengthwise growth, and from appositional growth which increases bone width.
Step-by-step explanation:
The growth of bone in childhood originates from the epiphyseal plate, which is located between the diaphysis and epiphysis of long bones. The epiphyseal plate is responsible for the lengthwise growth of bones. Chondrocytes on the epiphyseal side of the plate divide, with one cell remaining near the epiphysis and one cell moving towards the diaphysis. This process replaces cartilage with bone on the diaphyseal side, resulting in bone lengthening.
Bones also increase in width through appositional growth. Osteoblasts beneath the periosteum produce new bone tissue, while osteoclasts resorb old bone along the medullary cavity. This process not only increases the diameter of the diaphysis but also the diameter of the medullary cavity.