Have the most water balloons in the bucket before times run out.
Split children up into partners however many as necessary. Then put them next to their bucket of water balloons.
This is a relay race so have another bucket abouy 15 feet away.
The players have to put the water balloon between both of their backs and walk to the other bucket.
If your balloon breaks you must go back and get another balloon.
Set a time limit and when the times run out see which team has the most water balloons in their bucktet.