Recent studies show that children make substantial grains from lifting weights in strength and also in fat reduction.  Females, in particular, benefit greatly from weight lifting due to the fact that it helps build bone mass, because females are more prone to osteoporosis. 

Children can weight train safely without damaging fragile bone growth centers.   Most injuries to youth athletes occur at the ligaments and tendons.  A well designed strength training progression will strengthen the ligaments and tendons.