Just the thought of it, makes you cringe, having kids lift weights? Come'on, that's not good for them. Or is it?
In all my years in the business, the question that gets asked to me the most by parents is, "when can kids start lifting weights and exercising?" and I always answer it with these questions to them. Are you ok with your kids going to a play ground and climbing on monkey bars? are you ok with your kids running up and down a hill? are you ok with your kids jumping on or off things in the playgroung? Then you should be ok with your kids lifting weights and exercising. So yes, having a little kid lifting dumbbells, doing plyometrics, sprints, or any good exercise, is great for them!
But before you jump to conclusions, think about this, what's better for the joints, a kid lifting himself up and swinging back and forth and up and down on a bar (lets say the kid weighs 50 lbs.) without any technique, or a kid lifting or pulling 8 lb. dumbbells? The answer is, lifting the dumbbells is much better for them. Here's another one, what's better for the joints, a kid jumping off the top part of a playhouse or any other high thing they normal climb on and jump off from, or a kid doing plyometrics (that's continuous bounding, similar to standing long jumps)? the answer is, doing plyometrics. You have to realize that controlled movements with less weight is better for the kids, and adults too. So you just have to get it out of your head that just because a kid is doing weights or exercises, that doesn't mean his doing something bad for himself or his joint, rather he's doing something great for himself and he's saving his joints.
Though I must add, and this goes for anyone, kids or adults, or even elite athletes, doing improper technique in anything is not good, so when I say weights and exercises, I mean the proper weight and the proper technique.
Now go get those kids off the Ipads and start getting them lifting weights and exercising, no matter what age they are!