The answer, according to Michael Horowitz, MD, a pediatrician at Mount Kisco Medical Group, is…when your child is no longer a child. “Adolescents shouldn’t do any competitive weightlifting, power-lifting, or bodybuilding until they’ve reached their full skeletal maturity,” Dr. Horowitz says. When is that? “That age varies. The only way to know is to visit your child’s doctor.” Lifting heavy weights before a child has reached skeletal maturity can cause damage to the growth plates, which don’t fuse until a child stops growing. “If you damage these,” Dr. Horowitz says, “it can affect growth.” However, he says, light hand-held weights, “no more than five to ten pounds,” are okay.