Only one time ever I didn't provide food for the parents when I expected them to stay. I think you should provide it if your expectation is that the parents stay and it's not a drop off party. The reason I didn't provide is cuz it was at Potbelly's, all the kids got boxed lunches. I provided free drink and chips to the each parent staying, but they had to get their own sandwiches. I didn't feel good about that. Never did it again.
At a pizza party, I esepcially would not skimp on providing pizza for the parents. Get their cheapest option if you have to. But my advice is don't have a non-drop off party wtih a meal and then not feed the very people you are telling can't leave.
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