Man, after having gone back and re-read them as an adult, it's only barely a kids series. Animorphs went hard in the paint with the horrors of war angle.

Another good example is Terry Pratchett's kid-oriented books (e.g., the Tiffany Aching Discworld books, the Johnny books and the Bromeliad trilogy). He never wrote down to children. These books weren't really much different from his other books for an adult audience, although the plots were simpler, tended to focus more on children characters, and the morality was less ambiguous (as it can be in real life)). But as a big fan of Pratchett, I enjoyed these "children's" books no less than the others.

There is a scene in one of the books where the narrator finds a sliver of flesh still stuck in his teeth from when he was fighting in tiger form, and that isn't a particularly gruesome scene in comparison to the rest of the books, just to be clear. Harry Potter's later installments come close but Gravity Falls and Adventure Time aren't even in the same league. I do absolutely agree with your basic point though - I also greatly enjoy all of these series watching or reading them with younger family members.