It makes absolute sense, hhunter.
I know, I came from a "clean your plate" upbringing (very pervasive in the 50's/60's). I eventually got to a point with my own son where my attitude was "eat what you can...but no 'goodies' unless you finish the healthy stuff." My son has the large build prevalent in our family, but is not obese by any stretch. For that matter, other than a very slight "tummy", he's not even overweight.
The lesson I learned all too recently was that if you eat right, if your body gets enough nutrients, you won't crave junk food. With a healthy enough diet, a little sweet goodie here and there won't throw your weight into a tizzy. The problem with our diet is that it tends not just to be high in calories, but low in nutrition. And lifestyle is a major consideration. My grandmother's delicious cooking was great nutrition for busy, hard-working farmers in western Asia...but translate that same diet to a more sedentary, office-centric major city American lifestyle, and you can see where our "secretary's spread" comes from.
We need to stop thinking about "diets" and more about lifestyle. You've probably heard it all...whole grains over refined...seasonal, local and preferably organic...good fats/carbs vs bad fats/carbs...but you know what? When your body gets the nutrients it needs, you crave less other stuff, you have more energy and hence become more physically active, your mood improves...in other words, it works.
And just a tidbit of advice for the day - read those labels on packaged foods! You'd be appalled at how much sodium (let alone sugars and "bad fats") are hidden in some of them.
Kids are only as responsible as their ability to pay for or otherwise obtain food outside of their meal portions. Educating them to begin with is all-important. And providing "goodies" that are high in nutritients rather than empty calories is also a good step.
Last resort? If a child, given parents who provide sensible food and education, still chronically overeats, it could be a chemical or other imbalance in the brain. There is a center of the brain that controls satiety, and if it is somehow damaged, the person simply does not know that they are full, and they continue to eat. Again, rare...but in the event of morbidly obese pre-teenagers, it has to be looked at among the possibilities.