Disney's family fun has a cute way to take rocks and turn them into pumpkins using orange paint, a black marker, a stick and some glue.
Good for ages 5 and up.
Get the instructions here:
http://familyfun.go.com/crafts/stone-faced-pumpkins-669243/
Get the instructions here:
http://leisurelanelegers.blogspot.com/2008/09/pumpkin-rocks.html