It's a common myth that strength training stunts children's growth. As a pediatric exercise physiologist, I am regularly asked about this topic. Strength training is absolutely safe for children with proper instruction and light resistance, strength training improves bone strength, muscle strength & endurance, improves body composition, and even self-esteem!
Resistance bands are a GREAT piece of equipment for children and perfect for introducing new strength training exercises. It is important to start with exercises that incorporate large muscle groups, let's use squats as an example.
Chose a "light" resistance band (usually yellow or green bands indicate light resistance). Step both feet on the center of the band. Feet should be about hip width apart. Hold one handle in each hand, start with hands at shoulder height. Now we're ready to squat. Slowly bend at the knees, pretend to sit in an imaginary chair, bottom pushes back, and knees bend about 90 degrees. Your hands should stay level with shoulders, then return to stand. That's one! Try 2 sets of 10 reps. Talk to your children or students about reps and sets, you can even use it to explain multiplication (or addition for younger ones).
It's recommended that children get 60 minutes of physical activity everyday! 15-20 minutes of strength training should be included three times per week as a part of those 60 minutes!