Is it my place to tell my wife how to properly feed her own children?

I have 13-year old twin stepsons since I married their mother last year. My wife and I make decent money but we run out of food too quickly for my liking. One of the boys in particular gained more than a few pounds. He can eat an entire Oreo pack in one sitting.My wife keeps insisting that growing require different food portions than adults(and she added that I won't understand until I become a parent). But I can't help but to wonder if my wife is too lenient on them as far as food goes. That's why these kids are so FAT. Any tips?