Ways you can help your child improve muscular strength and endurance:

Encourage climbing, go to the park/playground, monkey bars, swinging, taking walks, jump roping, play tag, have a race, build an obstacle course and time how quickly your child can run through it, time your child running around the outside of your house, jumping on the trampoline, sign up for a 5k as a family, etc... ECOURAGE! ENCOURAGE! ECOURAGE!