This is a super easy and fun art activity for both kids and adults. My 5 year old daughter loved revealing the hidden pictures I would draw for her with white oil pastels. She also really enjoyed making hidden pictures for me to discover.
How-to: draw out a design with white oil pastels on white paper. Below are the ones I used, but any brand at all should work. I used watercolor paper, but you can use regular white paper as well. Then paint on the paper with watercolors to reveal the picture below!
I brought this project to my daughter's Kindergarten class. I drew on different Halloween pictures with a white oil pastel in advance and the kids loved revealing the hidden images. I love how different and unique all of the pictures turned out!