I hated to waste the money, but the values in that new book I bought were so awful I decided not to finish reading it. I tossed it. You needn't preach. Your example will say more than your speeches. A more difficult problem arises when a child is given a frightening book.
Many children have nightmares, and are too sensitive for upsetting books.
If I knew the book was too frightening for my child, I would ask the teacher if she was willing to sit up with my child every night until the nightmares ended. Teachers who are not sensitive may not understand how some books affect sensitive children. If the upsetting part is based on some sort of sadness, allowing the child to help can ease some of the fears. A book about a homeless child can lead to conducting a food and clothing drive, for example. When the child helps to alleviate the suffering, he often feels less devastated by the problem presented in the book.