The Chronicles of Prydain is the ultimate 'growing up' series. While a lot of 1960s fantasy feels dusty and formal, Lloyd Alexander’s writing stays lean and human.
It’s the perfect antidote to 'brain rot' content because it demands a bit of emotional investment. You get the magic swords and the scary villains, but you also get a protagonist who has to learn that being a hero is mostly about showing up and doing the right thing when you're tired and scared.
If your kid liked Harry Potter but found Tolkien too dense, this is the sweet spot. Just be prepared for some big feelings when they hit the final chapters of the last book.