My afterschool tutoring group has recently been working on identifying Main Idea and Theme, specifically CCSS.ELA-LITERACY.RL.3.9 - Compare and contrast the themes, settings, and plots of stories written by the same author about the same or similar characters (e.g., in books from a series).
To help my students understand what theme is, I used this little acronym I've seen all of the Internet: THEME = THE Message. The kids thought this was so neat, and I found it really helped them remember what Theme is and how it differs from the main idea.
After introducing my students to theme, I went over some of the basic themes found in children's literature. To help, I created these cards that we hung around the classroom after our discussion. These cards would be great to keep up year-round. After reading a book as a class, decide which theme it fits under, and then, post the cover image below the poster.
You can download them for FREE here! A version with white backgrounds (to save on ink) is also included. Enjoy!