You really can't go wrong with animals. Kids love them. There's so many to learn about. And you can tie art and science together by talking about animals, habitats, life cycles,etc. You can also tie in to social studies by looking at where in the world different animals are found, and how people around the world make art about animals because they are beautiful or scary or symbolic. Here's a look at some things we've been working on K-2 in My Blue Art Room (and we've been so busy the poor blog has been a bit neglected- on the other hand, we're in the PA top 10 on Artsonia right now... guess where my energies have been directed....)
"Dream Carver" by Diana Cohn, and then planned an imaginary animal to create.