Purpose: This review examines the effects of physical activity and exercise on bone mass/density [Bone Mineral Density (BMD), Bone Mineral Content (BMC)], bone size, and fracture risk in children and adolescents of both sexes.

Methods: This is a narrative (non-systematic) review. A literature search was conducted in the PubMed database up to August 2025. Studies evaluating the impact of exercise programs on BMD, BMC, bone size, and fracture risk during childhood, adolescence, and later in adulthood were included. Results: Most studies reported a significant increase in BMC, aBMD, and bone size in children and adolescents who participated in exercise programs compared with control groups, with the pooled evidence indicating that these effects are concentrated in prepubertal children. Furthermore, regular physical activity during childhood and adolescence was associated with a reduced risk of fractures not only during these life stages but also later in adulthood. A transient increase in fracture risk during the first year of intervention has been reported, and some trials found no effect on fracture incidence. Conclusions: Physical activity during childhood and adolescence enhances bone mass and bone size and is associated with a lower risk of fractures across the lifespan. These findings support the integration of exercise programs for children and adolescents as a preventive strategy for fractures and for improving bone health.