Anonymous wrote:But wouldn't that be four pies (8 slices per pie/16 kids)? The reason I asked about the parents is because they will have to drive to the location of the party and it probably wouldn't make much sense to leave. I don't want to look cheap and not offer food/snacks to the parents as well.
Yes. Your math is better than pp. (Cutting 16 slices doesn't make the kids any more full I'd add.)
Pizza is cheap. If you think parents might stay, "over order" and worst case you have leftovers to send home with friends and family or even give to the event site people running the bday party (we do this all the time and they are quite appreciative in the staff room!) Have fun!