With all the candy available at a Halloween party the little ones might have a lot of stored up sugar energy. The Sunlight, Moonlight game is a great way to get them running around and might drain them of at least some of that liveliness. Also, since it is just a Halloween version of the popular Red Light, Green Light game most if not all of the kids will understand the rules quickly.
Explain to the kids that for this game they are all little vampires who can move around freely during the night but must stop and hide from the sunlight. Pick one person to start the game as the caller and position all of the other kids on a line about 30 yards away from the caller.
To start the game the caller faces away from the children and yells Moonlight! At this point the kids can move toward the caller as quickly or slowly as they like. The caller then calls out Sunlight and quickly turns around to face the kids. As soon as the caller yells Sunlight the kids must stop instantly and mime covering themselves up to hide from the sun. If when the caller turns around they see any of the children moving or not covered up, those kids are sent back to the original starting line.
Continue play until one of the little vampires reaches and tags the caller. At this point the winner becomes the caller for the next game.
Tip: If you have kids of varied ages playing, consider having multiple start lines with younger kids closer to the caller when the game begins.