Still not the librarians choice to make..
So where does the librarian draw the line? This is 3rd grade, not kindergarten.
Op, no I would not be upset at all. Established, western world beliefs such as Santa, I would expect the librarian to uphold the secret just in case. But not fairy tales or cartoon characters or characters in fictional children's literature.
By 9 years old, children are intelligent enough to start really exploring literature in depth. They start learning the differences between short stories and novels, fiction and non-fiction. Mysteries and fairy tales.
Now back to my response to C.Ann.
Where does the librarian draw the line? How about Johnny who believes that transformers are real? Or Stevie who believes that Luke Skywalker is real? Or how about the Universal fanatics? Does that mean the librarian cannot discuss the Cat in the Hat or the Grinch without revealing that they are fictional characters? How about Spiderman, Hulk, Popeye, Scooby Do, Dora, The Simpsons and Spongebob, all characters at Universal that some child may believe are real?
How about Harry Potter? Should the librarian pretend that the wizarding world is real just in case some family allows their child to believe that Hogwarts is a real place? That would go over well with some families where HP goes against their religious beliefs
What fictional children's literature is it ok to discuss that the characters are actually fictional by 3rd grade?