Young children are such a bundle of energy. A short "exercise class" not only helps their large muscle development, but it can also be a sanity saver on a long, rainy day indoors. You'll feel better afterward, too!
Encourage your child to follow your lead as you exercise together. Try touching toes, running in place, swinging your arms, and stretching to the ceiling. Exercise to music, pass a ball back and forth, or twirl a long ribbon in the air. For a change, let your child be the leader and you follow his example.