White painted stones by Natasha Newton - These would make a nifty place card. Just hand your guests a business card with a matching design on it. Then they get to match the card to the rock at their place. They could then take the rock home as a keepsake.
Homeschool art program Another painting on rock activity. It doesn't have to be this fancy and complicated. Let children to try something new. Encourage them to try creating new pattern, color on rock.