> Others were books that sounded religious in nature (e.g., I recall a book from the Christian publisher, "Zondervan") which is understandable for U.S. public schools.

Is it understandable? I don't think I'd be alone in saying that I'm pretty uncomfortable with a book being banned from a public elementary school library just because it has a religious angle. I don't think it's a reasonable interpretation of separation of church and state to say it would require outright excluding religious books from a library.