We "do art" once a week for about an hour and are using The Polymer Clay Techniques Book to get our feet wet. Based on the suggestions, we started out with just a few simple supplies: ceramic tiles, rolling pin, sculpey clay set (10 colors), exacto knives. Our first lesson was learning some basic techniques, then playing with whatever technique appealed to us.
The only thing we've ever done like this is playdough, and that was QUITE a while ago - like when they were in pre-school. And we NEVER mixed colors. EVER! Now that they are older (11th and 8th grades) I'm looking forward to seeing where their imagination, skill, and personality will take them in this art adventure.