For anyone wondering if the tradition of philosophically transformative middle grade SFF series is being continued by more recent authors, the answer is yes: most specifically, Wings of Fire by Tui T. Sutherland (who also, under a different pen name, wrote some of the Warrior Cats books). The main story, which follows a bunch of young dragons as they deal with prophecies, magic, friendship, love and belonging, is told in three series, each consisting of five books, all of which I read aloud to my son at bedtime over a period of several years. Though also funny, colourful and moving, the core themes go harder than they have any right to, and by the end, Sutherland - like K.A. Applegate and Kathryn Lasky before her - is not remotely in the vicinity of fucking about.
Specifically, to give a breakdown of the themes in each book:
Series 1: The Dragonet Prophecy
The Dragonet Prophecy - What if you were raised by abusive caregivers who lied to you about your origins and who want you to be a warrior for the cause, but your greatest strength is kindness.
The Lost Heir - What if you were forced to confront the terrible cost of fighting vs the imperative of survival vs the burden of autonomy, and also you learned you'd accidentally killed your own father.
The Hidden Kingdom - What if you were told your whole life that you were lazy, unwanted and useless, but all the things your abusers disdained are actually your greatest strengths, and you succeed by embracing what they failed to value.
The Dark Secret - What if you find the home and the family you've always wanted, but your dad is a war criminal, your people are bent on genocide, and you have to choose between your own potential belonging and what you know to be right.
The Brightest Night - What if the single uncompromising principle you carry through war, betrayal and horror is the hope that people can be better, and then your hope wavers. What if you choose hope anyway and, in so doing, make it into a different sort of prophecy.
Series 2: The Jade Mountain Prophecy
Moon Rising - What if you had a secret about yourself that gave you legitimate grounds to fear that you'd be hated, killed or harmed if you disclosed it, such that your only confidant becomes someone dangerous. How do you learn to accept yourself while still staying safe?
Winter Turning - What if you've been raised in a high-control caste system but are starting to question your parents, your society and your role in life.
Escaping Peril - What if you're a former child soldier who was once manipulated into committing atrocities by the abusive monster who claimed to be the only person who'd ever love you, such that you still, despite everything, desperately want to please her? What if you struggle to be good anyway, even when almost everyone else is afraid of you?
Talons of Power - What if you were terrified of your own power, which you've been told can so easily make you a monster, but a bigger monster is threatening everything and everyone you love, forcing you to invent from whole cloth the philosophical thesis that power is inherently neither good or bad, and that what corrupts is feeling entitled to use it without check or consequence?
Darkness of Dragons - What if you were the hyper-competent, hyper-vigilant, clever child tasked with stopping a war, and the ultimate key to doing so is to force everyone to confront their shared identity and abandon historical prejudice (which was, itself, founded on deliberate propaganda).
Series 3: The Lost Continent Prophecy
The Lost Continent - What if you were the poster child for the model minority myth in a highly policed society, convinced that if you just obey the rules and do as you're told, you'll be safe and protected, only to have this illusion brutally ripped away and eventually conclude that oppressive systems cannot changed by internal reform; they can only be torn down.
The Hive Queen - What if you belonged to the oppressive majority in a bigoted society but came to be emotionally and politically allied with the oppressed. How do you unlearn the privilege you still have (even though you've also been somewhat outcast within your own majority) without denying your own identity or succumbing to self-pity?
The Poison Jungle - What if you're part of a hidden minority whose members are all survivors of an attempted genocide, raised in what is functionally a terrorist cell to take revenge on the people who tried to exterminate your kind. How do you unlearn the extremism of your upbringing in order to both exist as a person in your own right and choose a path to the future that doesn't involve an endless cycle of retributive violence? (And also you're a lesbian.)
The Dangerous Gift - What if you were raised in the dragon-world equivalent of a white supremacist society, hateful and angry and terrified of everyone you've been told is an intrinsic danger to your very existence while also being your inferior. How do you unlearn the bigotry of your raising and steadily become a kinder, better, stronger person in a way that acknowledges that transition instead of pretending it never happened?
The Flames of Hope - What if the open wound at the heart of the world was the twisted legacy of empire: centuries of genocide, violence and warfare that continued to self-perpetuate long after the initial cause was forgotten, because that's what cycles of violence do. What if you reached through time to the very first victim whose anguish started the cycle and offered them comfort, and in return, they gave you mercy. What if you were a fully grown adult reading the denouement of this book aloud to your child while actively weeping.
Like! I cannot emphasize enough how this series is rooted in the emotional thesis that some parents/caregivers are abusive, that it's good to ask questions, and that even if bad things happen to you, you still have a responsibility to be kind to others, because hurt you don't deal with becomes a generational inheritance, and then it just... makes that bigger.
The point being: middle grade books that make kids think about these issues are actually doing such important work, and the fact that they might be about owls or dragons or warrior cats or shapeshifting aliens doesn't make them silly; it's what makes those concepts accessible to the intended audience, not just by disguising the difficult bits in something cool and fantastical, but because the horror would cut too close without them.