Paint Trays are a great idea as they keep the mess inside the box rather than all over the table. It is still a good idea to put some newspaper underneath it to catch any stray splashes. We made a paint tray for the marble painting which had four sides (to stop the marbles from falling out, this one is open at one end so that if you want to you can get your hands inside close to the paper.)
1. Cut off the open end of the cereal box.
2. Cut away the front or back side from the box. You now have a paint tray!