Tummy for this, tummy for that

Yesterday, me and my friend took our children on an adventure, which included a stop at McDonald's. We're all sitting, eating, and chatting, except her little boy won't eat. He's having a great time, but would rather talk about eating cookies than eat his meal. His mother asks him several times to eat his meal and then he can have a cookie, and he tells her that his dinner tummy is full but his desert tummy is hungry!