Objectives: This 3-year follow-up study examined associations between physical activity and bone mineral content (BMC) and whether physical activity augments BMC accrual. Study design: Participants were 370 children (mean age baseline 5.3 years, follow-up 8.6 years). Physical activity was measured using 4-day accelerometry. BMC was measured using dual energy x-ray absorptiometry. Results: After adjustment for baseline BMC, age, and body size, mean physical activity predicted follow-up BMC at the hip, trochanter, spine, and whole body in boys and at the trochanter and whole body in girls. The variability in BMC explained by physical activity was modest (1% to 2%). However, based on a general linear model with adjustment for baseline BMC and body size, children who maintained high levels of physical activity accrued, on average, 14% more trochanteric BMC and 5% more whole-body BMC relative to peers maintaining low levels of physical activity. Conclusions: This study suggests that maintaining high levels of everyday physical activity contributes to increases in BMC in young children, particularly at the trochanter.