I have a chunky 9 yr old granddaughter and she became even chunkier after 6 wks of staying indoors and doing crafts and artwork w/other grandma. I kinda freaked when I saw her and we had a good long talk about weight. Short story, eat 3 meals a day as much as you want, 2 snacks. Pay attention when you eat, enjoy it and be active at least one hour a day. Oh yeah, and "stand up straight and suck it up".
Actually a much more effective strategy for keeping weight down is to making a habit of NOT eating meals, and of only eating a little bit at a time when you're hungry. Big meals stretch your stomach and get your liver producing large amounts of bile -- both of which will tend to make your eat more the next time you eat. The other problem with "meals" is that they tend to be planned events, which occur at a certain time regardless of whether any or all of the participants happen to be hungry at that time, and also encourage a mentality of "eat now, because soon it will all be cleared away and no longer available" (translation: eat more than you really want now, because if you don't you might get hungry later). Anyone who has trouble controlling their weight should firm policy of never eating except when hungry, apart from rare special occasions.