The aim of this study was to investigate whether climbing in children leads to the development of upper limb strength and endurance, and changes in body composition. Fifty young climbers aged 10–17 participated in an 8 week climbing program. Metres climbed were used as a factor to assess the effect of climbing. Two groups were ex post formed with a limit of 320 metres climbed. Boys and girls from the group that climbed more metres significantly increased their performance in bent-arm hang time (boys from 35.1 ± 3.9 s to 48.4 ± 4.4 s; girls from 18.9 ± 3.9 s to 24.4 ± 4.9 s) and grip strength related to body mass (boys from 0.65 ± 0.03 to 0.71 ± 0.03; girls from 0.52 ± 0.03 to 0.57 ± 0.03). Significant changes in the ECM/BCM ratio (extra cellular/body cellular mass) were found in the group that climbed more metres (boys from 0.88 ± 0.10 to 0.85 ± 0.09; girls from 1.00 ± 0.09 to 0.94 ± 0.09). There were no changes found in body fat in either group. The findings suggest that a climbing program with higher volume of metres climbed can influence grip strength, upper body muscular endurance and the amount of relative body cellular mass.