The challenge is to build the tallest tower out of their stash of paper cups. This is best played as a team game- 2 teams or more if yours is a large party. Have maybe 5 kids on each team- no more as they won’t be able to cooperate as well and that can detract from the fun.
You should 20 to 30 cups for each team– they need this many to build a stable base for their towers, but unless they’re really young let them figure this out for themselves. Stability is also better on a hard surface like a wood floor or concrete, not a carpet.
Tell the teams that the tallest tower wins, and pull out your watch so they get the idea they’re being timed, but don’t indicate how long they have- that way you can stop the game when you see their interest flagging.
Paper cups are significantly more challenging for tower building than blocks. They fall down easily, so warn them about that problem. They also have one closed and one open end the kids have to take into account. They’re tapered where blocks are generally square. It’s a different ball game and that’s what makes this seemingly simple task a good party challenge.
Thanks to the folks over at zaneeducation.com for this activity that works quite well for a party.