It's something we do together once a week, and I've been reluctant to encourage muscle building. Recently, though, I was relieved to read a set of recommendations developed by the American Academy of Pediatrics and the National Strength Coaches Association. Supervision and regular review are particularly important to be sure that, among other things, the lifter controls the weight, uses full range of motion, isolates muscle groups, and never holds his breath. Instead, use about 12 for the upper body and 15 to 20 for the lower body. - To make workouts harder, increase sets of repetitions before increasing weight. Training should not concentrate on one set of muscles.
Heavy weights can damage immature bones and joints.
Put another way, I think the experts are saying that developing good muscle tone is healthful for anyone of any age.