I love this idea I found on Pinterest, and it's a great activity for any age. I want to do some myself with watercolors and doodles around the letter!
You can print a letter or shape and cut it out, or use a pop-out from a stencil, like I did here. I taped it on the page with Washi tape, but any tape that isn't too sticky will work. Crayola paint seemed to work best for us, but you can also use crayons and markers to cover the page with color. Lift the letter or shape, preferably after the paint dries.