I go by the food guide as well for serving size and then cut them off - when their plate is done they are done. They have the option of a cookie when done if they want. Kids will eat whatever they get used to eating and if it isn't offered rarely ask. With so much obesity in kids even too much nutritious food becomes part of the problem. There are serving amounts per food category for a reason and we also have to consider the food the child is eating at home.