Here's another fun way to preserve children's artwork - take a drawing that particularly appeals to you (all the better if it's a fairly big one), write the child's name and the date on the back, and have it laminated. Presto, instant placement. They're cute, practical, and easy to clean (if the lamination is done properly they can go right into the sink).
(This is where I would add pictures of two really cute placemats if Blogger wasn't being such a pill, you'll just have to take my word for it.)
My kids love using placemats they've made themselves, and they make great grandparent gifts too.
Swing by Shannon's Rocks in My Dryer for loads of helpful hints from the parenting trenches, and don't forget to check out the incredibly giveaways going on over there (500 different ones and still going strong, one of them even by yours truly).