Our crazy weather has us in a melt/freeze rotation that has been providing lots of mud in the backyard at the preschool. The children quickly discovered that by either sitting in the mud or by simply scooping it up with their mittens they are able to create lots of pictures and designs by "painting" or making "butt prints" on the side of the garage (forgive the awful phone photos...I hadn't planned on taking pictures and I had to act quickly to catch the kids in action).
Once they've covered the wall, they clean their "canvas" by rubbing snow on it to clear the dirt. It is quite a process and so much fun for me to watch.
It should be noted that I do not recommend that the children try this at home without their parents consent and also that the parents have all communicated that they know it was a "good day" by how muddy their childrens clothing comes home to them.