I found this wonderful link (or link to a link) while browsing around this morning. What a great gift for your kids, and perhaps a way to introduce them to both art and charity.
Robots and Monsters ($25-$40) is an effort by artist Joe Alterio to raise money for the San Francisco AIDS Foundation, as well as the Pangea Foundation, which helps fight AIDS worldwide. For a donation of $25, you get a 6" x
6" signed piece of art, featuring a monster or robot, or both for $40.
Joe bases your piece on three words that you provide, such as "Green, tentacle, airplane."