training we ever get in our lives is the strength we gain on the playground. i want to meet someone who is 40 years old who continued to play on the playground for 2-3 hours a day like when we were kids. trust me they would be a physically fit to say the least.
take the time out of your day to allow your kids to play on the playground. if you do not have time to go out to the park try doing little things like in this video to encourage them to use their bodies in a way that will help to make them strong. 