Photo by makelessnoiseCavemen chiseled on walls, but you can hold the sharp objects for this toddler project.
We call it rock drawing 101.
You'll need a rock, a marker and hopefully a kid (although we're stealing this idea from an adult, so feel free to use it as your own personal stress relief).
Essentially the same as drawing on paper -- with the added challenge of the texture and shape issue of each individual rock -- this is a heck of a lot greener then letting them make one scribble on a sheet of white paper then throwing it out (or even sending it to the recycling bin).
If you're brave, you can hand the kids a fine-point Sharpie like Annie at Apartment Therapy, but we'd recommend something washable for your kids.
When they're finished, they make great paperweights or doorstops (think Mother's Day gifts), or you can return them to nature.
What are your favorite green art activities with the kids?