How to keep a child busy for hours in the summer: DIY: Giant Ice Cube Awesomeness - filled with plastic animals, dinos, and such. And I'm sure you could put in food dye before its frozen to color it like the ice block in the photo.
easy art for kids foil painting // It also helps to add a small amount of dish washing liquid to your paint mix. Not only will that make cleaning up easier but it also helps the paint to stick to the foil better and not flake off when it dries.
Paint Bag Writing: Add some paint to a plastic bag, seal it up & spend the afternoon with your kids drawing designs through the paint. Using a Q-tip instead of your finger to avoid tearing a hole in the bag.