I have thought about a homemade ice cream theme but am not certain about that idea. All suggestions are appreciated. They can also do the same with the beverages, you could have coffee and juice, but they could bring thier own coolers with pop and beer or any other beverage that they may want. That would take a lot of the expense and work off of you. It is a bit more casual than having the whole party in your yard.
People can come and go as they please.
Set up grills, and tables for side dishes, plates, cups, etc. Have another table for beverages, and another for desserts. On the invitations, tell people to bring a side dish, and any food they might want to grill. Set up some music or something, have some games for the kids like volleyball. Hot dogs, beans, salads, etc.