Cool the kids off with a homemade sprinkler. Take a 2 liter soda bottle, poke holes in it. Attach to a garden hose via a male to male adapter that cost less than 5 dollars at Lowes. Toss over a tree branch and let hang. You can adjust how the water sprinkles by adjusting the water flow. When the bottle dies just switch it out with another bottle -- no additional cost!