This amendment invites censorship.  It is unspecific about what topics will be considered "sensitive," meaning that teachers could get in trouble for not "warning" parents about content that many would view as neutral, such as gay characters, single parents, and more.  It also boils often-valuable reading material down to a few out-of-context words, phrases, or scenes.  Teachers are trained to choose material that will help students learn.  Don't hamper their ability to do so!  If parents want to stop their children from reading a specific work, or work that deals with a specific topic, let them do the research and decide for themselves what is appropriate.