Have the kids draw on sandpaper with crayons. Position the sandpaper right side down on a t-shirt. Place a piece of parchment paper or paper towel on top of the sandpaper to protect the iron. On cotton setting, iron the sandpaper for about 30 seconds. Gently lift one edge and make sure you have a good print before totally removing the sandpaper. Iron a bit more if you need to transfer more of the crayon.