RAD - weight training for kids

I'm no expert, and I can't refer you to any articles, but I have talked to some trainers and sports-medicine people who advised me about my own son after he experienced a very stiff elbow two years ago. (He liked going with me to the gym, and got a bit carried away with the bench press.) Their consensus was that children can improve their strength and overall fitness by doing some light resistance work (combined with appropriate warmups, stretching and cardiovascular workouts such as running, swimming, etc.). But they did not recommend allowing children to use heavy weights. First of all, they told me, children's skeletal systems (elbow joints, in particular) are not fully formed until after puberty, and may not hold up to heavy lifting. Second, heavy lifting tears down muscle fibers, which must be rested and repaired, using large amounts of energy. Rapid growth in childhood also demands high levels of energy, and the recovery process from heavy lifting may actually compete for these essential resources.
Finally, children's bodies do not produce the hormones necessary for the kind of massive muscle development people are usually striving for when they use heavy weights.

During winter or bad weather, when it's hard for him to play outside, my son uses rubber tubing and also does exercises that use only body weight (pushups, rope jumping, chinups, crunches, etc.). He also uses light dumbells several times a week to do squats and lunges (about 40 reps each), and these seem to increase leg strength and endurance.

But given the choice, we'd both rather have him doing regular kid stuff--running, throwing, jumping, wrestling, climbing, and otherwise using his body to the max in some kind of play. I think that's the best way to grow a strong kid. Chores, too. He has just finished splitting up the big oak tree I sawed down last month. At 100 pounds, he could barely lift the logs or swing the maul when he began. Now, after splitting two or three sections a day for two weeks, he's whacking away with a vengeance, and he likes it. He is actually nagging me to saw down another tree. He is convinced that this chore is making him a stronger hitter, and he feels like a real man, splitting oak.

So, despite the fact that I'm a big believer in weight training for adults, I'm wary of it for kids. But this is just my uncredentialed opinion, and I hope we find an expert to weigh in on this topic.