An 11-year study of more then 200 children challenges the assumption that lack of activity causes children to put on weight.
It suggests the effect is the other way around.. That getting fatter makes them avoid exercise. They found no indication that doing more physical activity had any effect on weight. But at the same time they don't want people to dismiss physical activity as an important part of a healthy life style.
The paper in the Archives of Disease in Childhood suggests programs to tackle obesity may need to focus more on food.