Here are two game ideas!
Crazy Olympics: Have a Crazy Olympics party and let the kids play silly games, such as the Backwards Crab Walk, Blind(folded) Leapfrog, Impossible Obstacle Course, Frisbee Golf, etc. Add a few ridiculous relay races for extra fun (pass the eggs, carry cotton on a spoon, one-legged race, and so on). The kids can also play Silly Sports. For example, they can golf with their feet instead of a golf club, or play baseball with a broom instead of a bat. They can even run the bases backwards.
Keep it Dry: Give each player a small object that changes when it gets wet, such as a stone, cotton ball, or a marshmallow. Players must try to swim from one end of the pool to the other without getting their object wet. The swimmer with the driest object wins.