My parents always included a little description of what would be served and the activities that would go on at our parties. For instance,
"Bring the whole family, we'll be serving hot dogs, cake and ice cream. The kids will play Pin the Tail on the Donkey, Simon, and Go Fish. We'll be near the tennis courts at XXX Park, or at ................. if the weather is bad."
Mostly we did stuff that wasn't a fortune, frequently if we were at the house, we'd just have a movie, hit a pinata and play a couple of games, 3 hours tops. They always invited an entire family, left it up to them how many showed up. No more than one present from each family, unless it was a birthday for twins.