I had an art teacher once who gave us all a potato and a carving knife. This was in the olden days when you could still pass out knives to young children in school without a special permit or safety waivers from all concerned stakeholders. We spent several class periods carving shapes into a potato half and then using it like a stamp by dipping it into tempura paint and then pressing it onto paper. We ended up with works of art on big sheets of butcher paper.
This post from Make Blog (originally in Craft Magazine) reminds me of that activity. Instead of half a potato, you use a rubber eraser to create your own rubber stamps. This saves you from having to deal with your potato slowly rotting and going soggy, which if I remember correctly, was why the potato activity only lasted a class or two.
This could be one of those afternoon activities to do with the kids while they are home from school during winter break. Don't just stop at the rubber erasers though. Bring out those vegetables and really impress your children with your knowledge of ancient art forms as you create wrapping paper for those Christmas packages that the relatives will never forget! Grandma may even secretly keep it and store it in her hope chest and occasionally brag on her grandchild by saying:
"Remember when little Bobby Sue hand stamped the holiday wrapping paper. With stamps he carved his own self! That boy is going to be something someday. Sure as the sun shines on these old bones."
[Image: Captured from "Hand-carved robot stamps": http://blog.makezine.com/archive/2008/12/handcarved_robot_stamps.html?CMP=OTC-0D6B48984890]