I would have calmly turned around, and explained to the child in terms he/she could understand, that all living things, including them, must and will die. It is the inevitable end result of our creation and the source of our ever present existential angst. And, lest he/she thinks they are guaranteed a long happy existence, further explained the mere act of crossing the street can result in your immediate and untimely demise, provided some unexpected horrible disease doesn't get you first. Oh, and then I'd throw in the fact that Santa Claus isn't real, and how their birth destroyed their mother's dreams and ambitions.
See? If one wants to be an epic asshole, and, in a twist of irony, be a far more petulant child than the one you're attempting to give the "what for", it doesn't have to cost you the out of pocket expense of a multitude of miniature pies.