Water Hoops will teach kids how things move in water and will teach them about angles. One person uses the buttons on one side to maneuver the ball into their opponent's hoop, and their opponent uses the buttons on the other side to do the same. Depending on how the ball moves in the water, a thicker fluid may be used to show that things move differently in fluids with different viscosities.

This toy might be a little pricey because of the way it needs to be manufactured to contain the fluid inside. The buttons may get stuck, and it would be difficult to disassemble the toy to fix those buttons because the fluid needs to stay contained. As long as everything stays enclosed, safety shouldn't be an issue at all.