Adults typically eat over 90% of the food that they serve themselves, but children only eat 60%. More than a third of what kids take goes uneaten. Why?
There are a number of reasons. One, kids when unprompted stop eating when they are full. Second, elementary school-aged kids are still in an exploratory stage with food. What they like. What amount of food will fill them up? Basically each meal is an experiment. Making mistakes is part of their food learning curve. They may serve themselves a food they realize they don’t like. Or they take too much food and get full before they finished. Left to their own devices they will sort this all out and more often than not they will not overeat.
Step in parents who encourage kids to clean their plate, don’t be wasteful, eat what you take, eat your vegetables, don’t be stubborn, and any number of other well-meaning messages that inadvertently teach overeating. When your child leaves uneaten food on his plate, he is just being a normal kid.