Start the game by hiding orange- to grapefruit-size water balloons outside and providing plastic pails for the children to collect the balloons as they progress.
Nearly any "hunt" variation will work. Try hiding clues with the water balloons that lead children to the next cache, and so on. Or, simply say "go" and see who can find and return the most hidden balloons -- without breaking them.
For older children, try playing hide-and-seek. Give the "hiders" water balloons and have one "seeker" start counting down from 20. When the seeker reaches zero, she tries to find those who are hiding. As the players are discovered, they can lob their water balloons at the seeker. Everyone takes turns seeking, so everyone has a chance to get wet [source: Fantastic Fun and Learning].