Weights for Kids

http://well.blogs.nytimes.com/2010/11/24/phys-ed-the-benefits-of-weight-training-for-kids/
"Somewhat improbably, from that scientific finding and other similar reports, as well as from anecdotes and accreting myth, many people came to believe “that children and adolescents should not” practice weight training, said Avery Faigenbaum, a professor of exercise science at the College of New Jersey."
"But a major new review just published in Pediatrics, together with a growing body of other scientific reports, suggest that, in fact, weight training can be not only safe for young people, it can also be beneficial, even essential."
The bottom line - their subjects benefitted from weightlifting.  The caveat - I did not consult the study to see what training they did, but I don't need to look.  I know what works for my kids, and what will work for your kids.  The same thing that works for Olympic athletes, scaled the ability and experience of your kids.

The article continues:  "Consequently, many experts say, by strength training, young athletes can reduce their risk of injury, not the reverse. “The scientific literature is quite clear that strength training is safe for young people, if it’s properly supervised,” Dr. Faigenbaum says."
When should they start?
“Any age is a good age. But there does seem to be something special about the time from about age 7 to 12. The nervous system is very plastic. The kids are very eager. It seems to be an ideal time to hard-wire strength gains and movement patterns.” And if you structure a program right, he added, “it can be so much fun that it never occurs to the kids that they’re getting quote-unquote ‘strength training’ at all.”"
This last quote is absolutely spot on, and is the basis of CrossFit Kids (www.crossfitkids.com).