Painting with ice. All you need to do is fill an ice cube tray with liquid water color and water. Stick a strand of tape directly on top of the ice cube tray. This is so the toothpicks will stay in place while freezing.
bubble painting: have the kiddos blow until they have a huge pile of bubbles, then press the paper gently into the bubbles, allowing them to pop on the paper (repeat the process with as many colors as the kids want) - the end result is amazing!