Explain that we have books for all readers, but not all of our books are right for every reader.
Let them know that no student is required to check out any specific library book, and we can help their student find something else they will enjoy.
If they want a book removed, let them know that you will notify your district librarian and your school administrator. Collect their information and more about their concern, but do not remove the book from your shelves.
See policy below - we have a process for book challenges, and must follow the policy. We don't make these decisions ourselves.