Thanks for all the great ideas! I'm thinking we'll go with painting flower pots (though I want to make sure the church school isn't doing them too, since a lot of kids also go to the day care and school run by the church). Everyone can do it, including most of the nursery kids (a lot of 3 year olds), and we can all do it together in the cafeteria. Then kids who finish early could make a card. I could have paint pens and regular paints. We did some crafting last winter for their parents, including painting, and they really liked that. Also seems like a pretty easy set up and clean up, and something any level of kid can do.
Thank you all for saving the day for non-crafty me!! This is such a relief to have figured out. Now I have more ideas for this year's Christmas gifts too!
ETA- if anyone has any suggestions on the cheapest place to get materials, let me know. I haven't started checking prices yet, and I still have time. I'm thinking my best bet may be one of the craft stores (Michaels, Hobby Lobby, etc) with one of their coupons if they sell little pots.