While looking at the causes of child obesity I found this:

Lack of physical activity: Computers, television, and video games conspire to keep kids inside and sedentary, which means they burn fewer calories and are more likely to gain weight. Concerns about the safety of outside play and a reliance on cars instead of walking – even to the corner store – don’t help matters. By preschool age, many kids are already lacking enough activity, which often translates into poor exercise habits later in life.