I am overweight in present. But guess what? Unless your kid INHERITED some metabolic disbalance the amount he/she is eating will not affect his weight - at least if he's not eating 2-3 times his body requirements - which is a hard thing to do for a kid. And if he inherited your problems, they are not going to be corrected by restricting what (mostly) and how much he's eating. In any case, you should consult with a dietologist before attempting anything, because restricting the kaloric intake might be a very harmful thing to do for a growth development.