Sounds like a noisy good time! I'd go with tacos or sloppy joes, baby carrots with dip, some kind of fresh fruit (like grapes, maybe, or a fruit tray or fruit salad), and offer water bottles along with a variety of soda. For dessert, resist the temptation to get a big sheet cake from the store - enlist a few other parents to bake batches of brownies or cookies.

Or you could serve chili, and have cornbread or tortilla chips along with it. Hot dogs would be okay, if you offered some toppings more interesting than just ketchup and mustard - think chili-cheese dogs, maybe. Or offer some sausages along with them, bratwurst-type things, to up the class level a bit, because you can't treat them like little kids!

Good luck! Have fun!