Background: This study includes an investigation of lower-limb muscle strength and physical activity among children in Japan and China, with the aim of promoting children’s health. Methods: A total of 564 children (300 boys, 264 girls) aged 9–12 years from public primary schools in Tokyo, Japan, and Jiangxi Province, China, were included. Height, body weight (BW), hip adductor and abductor strength, and toe grip strength were measured. The side-step test (SST) and timed-up-and-go test (TUGT) were performed. Exercise habits were assessed via a questionnaire. Results: Japanese students produced significantly higher values than Chinese students in SST (23.3–37.1%) and TUGT (6.6–8.0%), except among 11-year-old girls. Japanese boys aged 10–11 and girls aged 10–12 had significantly greater hip adductor strength/BW and toe grip strength/BW. Japanese students also showed significantly higher hip abductor strength/BW at all ages. Additionally, the proportion of children engaging in vigorous-intensity physical activity (VPA) was significantly higher in Japanese boys aged 10–12 and girls aged 9–11 than in their Chinese counterparts. Conclusions: Chinese students showed diminished lower-limb strength and agility compared to Japanese students. These findings highlight the importance of promoting outdoor play, particularly VPA, to improve children’s physical fitness and health, especially in China.

Background/Objectives: Previous studies have reported that Chinese elementary school children exhibit reduced lower-limb muscle strength, particularly hip abduction strength, compared to their Japanese counterparts. In this study, we examined the association of regular basketball participation with lower-limb muscle strength and motor performance in Chinese boys aged 9–10 years. Methods: A total of 97 boys in Grades 4–5 were recruited from public elementary schools and local basketball clubs in Shandong Province, China. Measurements included height, body weight, grip strength, hip adduction strength, hip abduction strength, toe grip strength, the side-step test (SST), and the timed-up-and-go test (TUGT). Participants were classified into three groups: a ≥1-year group (Grade 4: n = 19; Grade 5: n = 14), a <1-year group (Grade 4: n = 17; Grade 5: n = 14), and a control group (Grade 4: n = 18; Grade 5: n = 15). Results: After adjustment for grade, age, height, and body weight, both basketball groups showed significantly higher SST values than those of controls (adjusted differences: 3.078–4.649 repetitions; p < 0.05) and shorter TUGT times (0.642–0.779 s; p < 0.001). Grip strength was higher in the ≥1-year than the <1-year group (p = 0.010). No significant group effects were observed for hip adduction strength, hip abduction strength, or toe grip strength. Conclusions: In this cross-sectional study, regular basketball participation was associated with better agility and functional mobility performance in boys aged 9–10 years. These findings highlight the potential relevance of basketball-based multidirectional activities to the development of agility and functional mobility during childhood.