When we were children many of us would open our Christmas gifts and run outside to start riding that new bike or give the new baseball bat a swing. This Christmas you can get a workout and spend time with your children by heading out to play with them. A Harvard Medical School study found, playing with your children is an effective way of burning excess calories. Research found that by engaging in moderate play for 30 minutes, 155-lb. adult burns 149 calories. By ramping up the energy a bit and engaging in vigorous play, this same individual can increase his calorie burn to 186 calories. Just remember to get your kids something you both can play with outside!