I think some kids are just hungrier than others. Allie (5) could eat all day long. She generally eats 3 full meals, plus snacks between meals, and dessert after dinner. I give her lots of foods with good fats in them, lots of fiber, etc to try to fill her up, but she is pretty much always hungry. Is he very active? I find that Allie is much more active than Katie and generally much hungrier.