Your child should be getting in at least one hour of daily physical activity. Most of that hour should involve aerobic activity, but muscle and bone strengthening are important, too [source: Centers for Disease Control and Prevention].
You don't have to look at your child's daily dose of activity as a once-a-day event -- you can create other opportunities during the day.
Here's a trick Dawes uses for herself: note cards. Throughout your home, strategically place note cards with different activities -- using visuals when possible -- on the wall. For example, perhaps as your child enters his or her bedroom, he or she always passes a card that calls for 10 push-ups. Whether your child does the exercise or not is up to him or her, but if you wrap goals around those cards, you'll get to see if they're doing the trick.
Need some help selecting activities for those cards? Why not start off with push-ups, crunches or jumping jacks? Throw in some stretching exercises, as well, such as bending over while standing and touching your toes.