We didn't have structured events for our 5 yo's party at a playground. We just brought chalk, bubbles, hula hoops, balls and one of those parachute sheets.

I don't think it's weird to have a party for both kids at once; I've been to plenty like that.

For food we just did pizza, Clementines, watermelon and Pirate Booty (enough for everyone). No one ate the Clementines but the watermelon was a hit. Cupcakes for everyone for dessert.

We also gave mini fans as a favor. Also a hit.

I like the pinata idea.