http://www.joann.com/joann/catalog.jsp?CATID=cat1763
You should be able to buy the paints from Jo-ann fabrics right off this site.
I'm not sure, they may not ship paint, but it's worth checking.
I used their line for my cane and years ago, we did all the kids's hands on our little picnic table- they have some for every material, ceramic, even glass.
And they'll tell you which to use. And in each line of paint there is a clear coat. They're nice, inexpensive, and a lot safer to use around little kids than the types of paint you'll probably find at Lowe's.
These are made with crafting moms and grandmas in mind.
BTW, I love your idea and I just may steal that, lol.