Once every three or four months my son, Sam, grabs a cookie or a piece of candy and, wide-eyed, holds it inches from his mouth, ready to devour it. He knows he’s not allowed to eat these things, but like any 9-year-old, he hopes that somehow, this once, my wife, Evelyn, or I will make an exception. We never make exceptions when it comes to Sam and food, though, which means that when temptation takes hold of Sam and he is denied, things can get pretty hairy. Confronted with a gingerbread house at a friend’s party last December, he went...