Of course I found the idea on Pinterest which linked me to here. I chose to simplify it a bit.
All you need is:
Large paper plates
Red tempera paint
Green and brown construction paper
While the kids painted their plate, I cut out leaf shapes from the green paper and stems from the brown paper. After the paint was dry I glued the leaf and stem to the back of the plate. Voila! There you have a cute and simple fall craft for kids.