Printed wrapping paper
This was a hit for our school's annual Tree Sale, where we have a table of crafts for sale. Though I was working with 2nd-5th graders, even the youngest of painters could participate in this craft idea! You would just want to encourage very small children to use paint sparingly to avoid cracking, crumbly paper. Or use markers, watercolor, or stamps: we had some bundles printed by Pre-K kids using holiday-themed rubber stamps.
My group of crafters free-drew some sheets, but we had the best luck (and fun) finding things around the house to print with: apples, carved sweet potatoes, yarn wrapped around a flat-bottomed container, round spongers. We then used some of the decorated paper to make tree-shaped cut-outs, glued them to a kraft paper tag, and bundled up coordinated selections. We had extra tags to sell in small bagged bundles.