My daughter will be having a 6th birthday party on Saturday, and she wants a "Doctor Who" theme. None of her little friends are going to "get" it, but we are honoring that request, too, but modifying it a little to be "space" themed as well, since he does technically travel in space. Maybe make yours a "classic horror movie" theme?
Maybe you can borrow one of our ideas:
One of the games we are going to play is a variation of Frog Detective. In our game, the "Doctor" has to find the "mad scientist" who is turning everyone else into "robots." You pick a detective (or doctor, or monster hunter, or whatever), and give everyone else a notecard. One of the notecards is marked, and that person is the criminal (or mad scientist or monster or whatever). Everyone wanders around the field. If the (marked card) person touches you, you get turned into something (a fly, a robot, a zombie, maybe?) The detective has to figure out who the monster is before everyone becomes a robot or a zombie.