@Rebel- Agreed, I remember reading something about this.
As per the healthiness of this, I work as a medic, so until someone with an MD or RN shows up, I guess I'm closest thing we have to a doc.
- Weight lifting of light to moderate weights is positive, even for kids, but heavy weights and power exerices are bad, the can impact growth plates, and stunt growth. Young bones are also weaker than adult bones, they haven't had time to fully calcify and are soft (allowing for growth). Heavy weights could cause greenstick fractures, which are like stress fractures, but more extensive.
Mostly however, it's dangerous because kids are like anyone else who doesn't know how to use weights. I work out pretty intensively, 3-5 x a week with varying weights, and have spent a lot of time working on technique, both for results, and safety.
That said, this kid is recieving world class training, so I doubt they are doing anything to endanger his safety. It's possible he grows up to-- well, not up at all really since his growth plates could be damaged, but likely he'll be normal, if very strong.
For questions on kids fitness:
http://www.nlm.nih.gov/medlineplus/exer ... ldren.html