Then you yell and hit them every time they eat something off their diet. If I have kids (which I never intend to). Shame the fuck out of them every second that they are fat. When they sneak food, threaten calling the cops for theft. Portion their food for them before they get to the table. Pack them a lunch daily (weighing the food) then weigh them when they get home. If they ate more than you packed, guess what? The scale doesn't lie and they don't get dinner.