Freekidsbooks.org Is a cool website that I found to download PDF eBooks for your students. It looks to have a decent amount of books especially for a free resource. You can search through books by publisher, author, grade level, and even ESL.
I found classics like The Tale of Peter Rabbit and books on Feelings and Emotions as well as bullying.
While I did not stumble across any potentially offensive book choices, definitely be sure to follow the district classroom library policies and get the books approved as you would for a printed book.