Instead of nagging, set a healthy example. Don't give one child a diet plate while everyone else dives into fried chicken and chocolate cake. Make family meals healthy for everyone. Instead of collapsing in front of the TV after dinner, go for a walk or bike ride with the kids. In order to avoid rebellion and crushed feelings, when you talk to your children, focus on health, not appearance, and emphasize more activity, not less food.
Diets create feelings of deprivation.
For that reason they don't work for adults, and they won't work for kids either. Be realistic about your child's weight. Genes do make a difference. Research suggests that this kind of extra weight is not as much of a health risk as the kind acquired via too many snack foods and too many hours on the Internet. Genetically pudgy children may be healthier chubby than if they are forced to diet to fit in with slim peers.