Because whenever I buy them to go in lunchboxes they get snaffled and my older 2 DC are getting fat. They have good meals - balanced-ish and home-cooked but too much snacking on junk is causing havoc. So no more sandwiches and fruit in lunchboxes and no extras. I don't mind the off visit to the cake shop or the ice-cream van after school but nothing will be kept at home.
If they are hungry they can have cheese, ham, fruit, crackers, bread, I suspect they will find they are starving a lot less frequently than they have been.
How's that for a plan?