I learned this "craft" from our daycare provider which had Camila do it when she was quite young (2?). All you need is some paint (we used a combination of acrylic and whatever paint you use to paint wood, what we had at home) and a rock. Fortunately, the lady who used to live in our house until she died (at 95!) was a huge rock collector (mind you, not "pretty" rocks, just random rocks she gathered in the California desserts), so we have quite a few rocks around. You can paint whichever designs you want on the rocks, both girls chose to do ladybugs, but later Camila did a bumble bee as well. Both girls had a great time doing it, and after they're done I can put the rocks where they were before in the garden :-)
Mika's ladybug is the one above and Camila's, of course, is the one below :-)