In primary school (in Europe), we had a cafeteria, that served decent, regular meals, with one modest dessert. There were no vending machines, no child carried cash, only coupons for the cafeteria, tied to your name, entitling you to exactly one meal per day. There was also a smaller brunch at 10.

Why give children the option to make the wrong choice? If they were wise and disciplined, they wouldn't be children.