Special care must be taken to train kids. Please read the following articles for more information:

Weight Lifting and Kids
Stephen D. Ball, Ph.D., Nutritional Sciences
College of Human Environmental Sciences, University of Missouri-Columbia
Kids lifting weights? I know what you are thinking; strength training is dangerous for children. Many coaches, parents, and exercise professionals believe lifting weights is unsafe and not beneficial for children, despite the overwhelming research to the contrary. Read entire article at MissouriFamilies.org »

Strength Training andYour Child
Strength training can be a fun way for your child to build healthy muscles, joints, and bones. With a properly designed and supervised program, your child can improve his or her endurance, total fitness level, and sports performance. Strength training can even help prevent injuries and speed up recovery. Read entire article at KidsHealth.org »

Strength training: OK for kids when done correctly
Strength training for kids is OK. But bodybuilding is dangerous. Know the differences and follow these guidelines to keep your kids safe. Read entire article at MayoClinic.com »

Strength Training for Young Athletes
By William J. Kraemer, Ph.D. & Steven J. Fleck, Ph.D
The possible dangers involved in resistance training are related to inappropriate exercise demands placed on the child. Although there are general guidelines for resistance training, you must consider the special needs of each individual. In essence this means you must design a program for each child's needs that employs proper exercise techniques and safety considerations. Read entire article at DaveDraper.com»