Yeah I do that too.. even now, for days I prefer a certain food, then switch to the next favorite.
Always a poor eater, so its easier to have tiny meals every few hours. I would imagine I have a tiny tummy that refuses to let food in, and refuses to expand to allow me to have larger meals.
The massive hunger i feel at times, usually leads to me being totally FULL, even though i may NOT be satisfied with a few spoonfuls of food. To avoid feeling sick, i always have to stop eating.
As an adult I am aware of this, so i do it consciously. Kids may just stop eating when the discomfort sets in. Not sure.
Earlier I felt it was because of the gluten intolerance, but I'm gluten free now, and still cant eat enough.
Maybe its just one of those things we dont have enough reserch about . yet.
:-)