I checked out a great book from the library called Martha Stewart's Encyclopedia of Crafts: An A-to-Z Guide with Detailed Instructions and Endless Inspiration. It is exactly that, and I got the idea for this kid-friendly activity from there.
I failed to take pictures of cutting the stamps themselves, but it is really very simple. Cut a potato in half length wise as flat as possible (I actually cut each potato into 4 lengthwise slices), so as to get the most surface area. I had pretty average size potatoes, so my shapes were small. Use a small cookie cutter to cut out shapes from the potato. Since I didn't have very many small cookie cutters, I ended up cutting several of my own shapes, like the stick boy and girl, the heart, triangle and rectangle. It doesn't have to be fancy.
Pour a little washable paint into a paper plate, press the potato stamp into the paint, and Voila! I only had one color paint, but that was not a big deal to Grace. Be sure to have your little one wear a bib or apron, as paint is, by nature, messy.
Can you tell which card and paper are mine? Ben said we should make cards for somebody, so naturally, I made one or two for him!
Grace is already asking when we can do " 'tato stamps" again!