Here's a cool tip for a hot day from Parenthacks: have your kids paint the house with water:
All of the recent talk about spray bottles for summer water play made me remember something my mom used to do with me. She would take a paint brush and water and let me "paint" the house. Works like a cheap aquadoodle. This just bought me a good half hour of peace with my 2 year old. He painted my car, the driveway, the house, and even me!
We also used ice cubes like crayons to draw on the driveway. The teacher in me loves that it combines so many elements: sensory, art, dramatic play, and writing