Feel free to ignore the prior post, yours is a good fair question.
I would recommend you call some schools in your area. If you find one that does XMA, they can probably do a really nice demo for your party.
XMA focus is more on the flashy, gymnastic side of Martial Arts, it's not really useful for actual self defense (although the conditioning is excellent) but it looks really cool and kids would love it.
Good luck to you.
Undefeated in all of Asia!