I can't think of a single work of great literature that wouldn't upset an over-sensitive outlier. There is variation in sensitivity in any human population. Why should the extremes of the bell curve be catered to at the expense of the majority? If As others have said, if I was a parent, I would be furious if my child were being deprived the chance to discover and study critically-acclaimed works of literature because a classmate of theirs was over-anxious.
Many children crave to read books that move them in good ways or bad ways. It's a raw human desire. This is anti-intellectual nonsense akin to destroying a beautiful Italian sculpture so nobody else can see it just so it doesn't offend your eyes. Teachers do take into account the age of children when they set texts. They base it on the majority of that age group pitched to the average sensibilities of that age group - it's not like they are studying A Clockwork Orange at age 11 on the Curriculum (even though many young teens would have no problem with that!).
Great works of literature are great because they deal with themes like the human condition, overcoming adversity, heartbreak, tragedy, betrayal, revenge, war. Some are meant to evoke feelings of sorrow, revulsion, contemplation, disturbance, horror etc. I have read many novels in my life that have made me weep, be frightened, feel extreme sadness or despair - they were all wonderful books. I loved feeling those emotions. It's exhilerating. Those are normal emotions that come with discovering new things in life. I want to feel those emotions. The human population wants to feel those emotions. If they didn't, they wouldn't be such popular and loved great works of literature. They are formative to growing up and discovering things about yourself and the world.
Children and young adults throughout history have always read books with all sorts of themes some may find horrifying. Everything from The Iliad to Shakespeare's plays to Frankenstein to Treasure Island to Crime and Punishment to Tess of The d'Urbevilles is bound to upset at least someone. That's what literature is. These books are taught in curriculums all over the world. Most of the great classics contain material much darker than the book you are complaining about. Should children never be exposed to anything? Should they not learn about the atrocities of the Holocaust or great famines or war crimes? Should they not learn about genetic disorders or cancer or nuclear disasters? Should they not learn about slavery or the barbarity of ancient civilisations or how women were treated throughout history on the account it may upset one or two class members? There would be virtually nothing to teach.
And I believe the public consensus on the mental health issue in children is equated to children being massively over-coddled, everyday normal unpleasant teen emotions and experiences being pathologised as "extreme trauma", children having no resilience or exposure to discomfort or difference of opinion and parents overindulging and encouraging kids anxieties. The mental health crisis isn't being caused by children being exposed to critically-acclaimed and age appropriate great works of literature.