It's as if kids have a never-ending supply of energy. Just trying to keep up can wear you out, but that's not a bad thing. Playing with kids is as rewarding for you as it is for them. If you don't have any of your own, volunteering at a local church or YMCA will get you involved. Do you get active along with the kids in your life? How often? Any games or activities you find particularly invigorating?