Building Strength in the Young Athlete- General Fitness Calisthenics
Start with “General Fitness”. Make sure your child is proficient in basic calisthenics. Calisthenics can help set the simple movement pattern skills that will lead to more advanced and complex movements. 
Implement jumping jacks, push ups, pull ups, dips, lunging, squatting and skipping. You may need to modify the movements at first based on the child’s ability to execute properly. For example a kneeling pushup may be used before progressing to a full body pushup.
As your child progresses,  increase the number of repetitions and/or vary the movement, for example going from  two footed to single footed jumping and hopping.
Basic calisthenics will help your child establish a base of movement skills that will allow more complex athletic skills to be built upon ensuring better performance, endurance and reduce the likelihood of injury.
Aaron Thigpen is owner of Gamespeed Sports. For over 25 years he has been developing the athleticism of athletes from the ages of 8 and up. Check out this related article Will Lifting Weights Stunt Your Growth? What age Should You Start Lifting?