Split the kids up into 2 teams (any size is good). Have sheets held up over a line (could use a volleyball net to hold them up) to block the view of the 2 teams. Each team lays down 6-8 players. The remaining players on the teams then proceed to throw water balloons over the sheet. A judge keeps eye in case a player laying down in the playing field gets hit. Once a player gets hit they are out and can proceed to throw balloons. The team that loses all of their players laying down loses.