Answer:
LOL. Well first off if they are still refering to it as a "sleepover", I am assuming they are still rather young. Well, before they come over, you could set up a prank. Involve your parents. They will really know what kinda prank would be funny. For example. My step father is a state trooper. If I wanted to scare a friend, I would accuse him of something terrible, tell my mom (while he is watching) and have her call the "police" (step dads cell phone). Have him come over, "arrest" him and sit him in the car. Lol just an example.