When my six year old daughter broke her arm, we figured our big lake vacation was going to be a real test of her patience. Then a friend told us about DryPro Cast covers. They're essentially a super-thick latex mitten (or 'crab claw') that covers the entire arm or leg. Air is sucked out via a one-way valve to give it a snug fit, like a rubber glove. The device comes with a detachable bulb pump, but we usually just sucked out the small amount of air needed by mouth. Our daughter used it not only while swimming and bathing, but for water-tubing, rope swinging, and general sprinkler fun. She was able to submerge the broken limb completely. The covers are not indestructible, but the only thing I was ever worried about, and warned her to be careful of, was cutting the cover on a sharp rock. I actually purchased a second cast cover in case my daughter tore the first one -- she didn't. And it completely saved the vacation. I'm guessing these will last most kids at least one bone-mending cycle.