Plague is a game (probably from the New Games' Movement despite its grisliness) played with any number of people more than 3 although works best with about 10 or so. (Personally, I wouldn't encourage kids to play it - this is an adult thing, I think.) The game requires a squashy ball. It should be played in a confined space suitable for the number of people playing. A large room is ideal, so long as there's nothing to knock over and break.
The principle of the game is easy. Plague is passed from player to player until everyone dies (fun huh?). Someone starts off with the ball - it doesn't contaminate him/her; it's only 'live' after it is passed the first time. The ball is symbolic of the disease. If someone with the ball touches you, they pass you the ball. You must carry the ball in the nearest available place to where the person touched you. If they touch you on the foot, you should hold the ball in the crook of your leg: if your face is touched, you should carry the ball in your mouth, and so on. This should incapacitate you - in effect plague hampers your movements.
You can catch and pass on plague three times; after the third time, you must play dead, remaining in the exact spot and position you are in when you pass the ball on. The part of your body that becomes contaminated by each pass of the ball remains unusable. If you held the ball in the crook of your leg, then you must keep that rigid until you die. Injuries, therefore, accrue. You should also emit moans and cries relevant to the amount of pain you are in. Each time you get the disease, you should moan a little louder. The general moaning in the room should end up rather atmospheric.
One other thing. Play this game at night - and with the lights off. If you've got some Michael Nyman cds, put one on low in the background. Players must crawl and feel their way around (around furniture, over bodies (alive and dead)). It's not a fast game, but it is scary. You can't see - your leg is contaminated. There are moans all around you. You think you're safe, but something is crawling towards you - and you're trapped in a corner. You try not to breathe, but your leg forces a moan out of your mouth. The shadow crawls towards you ... stops, and shambles away... but not before it forces the plague into your armpit...
Clearly the game ends when everyone is dead.
Party game meets gothic horror. How much fun is that?!