We started with Molly Bang's When Sophie Gets Angry, which StoryBook Art tells us the author painted using "gouache". We were just using tempera paint, but the kids were delighted to notice that actually some of our Crayola-brand paints said "gouache" on the labels. So we had "the real stuff!".
A bit of planned activity is very helpful in getting past the post-Christmas cranky days, I'm finding.