My youngest son just turned 8yrs old.  His favorite thing to do, is to play baseballs. So we had a baseball party. First we sent out invitations that had a ball glove and ball on them(found at the Dollar Store).We wrote on the invitations that they could bring a ball glove if they had one.  My son already had the bat and balls. Then we decorated the dug out and the fence at the local ball field(which was free),with Birthday signs and baseball pictures. Then I made cupcakes that looked like baseballs, and had single juices to drink.  We had boys and girls show up, and they really had a great time playing a real ball game.  This party was really inexpensive, easy to manage, and easy to clean up.