It sure doesn't take long to wipe out the benefits of exercise. If the kids spend an hour or two playing a softball game and chase that with a bag of chips and a sugary sports drink, they're probably taking in more calories than they burn.
I made the kids sort through old toys last weekend and our donation pile turned out to be a mountain. And that makes me sad! It's not just the emotional attachment. It has much more to do with good ole parental guilt.