Two teams (facing each other), lots of balls/screwed up paper
Pick 2 people (1 to lead each team) and tell them only them what the objective of the game is - to have the LEAST number of balls on their side when the whilst blows.
After 2 minutes, stop the game & count the balls. Announce the result and ask the 2 teams who they think the winner is. Ask the rest of the Beavers what the objective of the game was - see how many of them knew, then see if the leaders told them !