Syracuse University has an exhibit at the E.S. Bird Library called Raising Rebels: An Exhibition of Radical Children's Literature. The exhibit includes biographies of radical activists as well as books with feminist, pacifist and radical themes. I was a little surprised to see 2 books by Leo Lionni in the exhibit, Frederick, and Swimmy. I used to read these books to my daughter when she was young. They are under the section: Imagination in the Service of Cooperation, Equality, and Peace.
You can read about this really interesting exhibit at their web site and look at digitized images of the book covers.