Might be because I remember the 90s so well... but I was fond of Aeon Flux, The Maxx, etc. In the 80s you had Heavy Metal... and When the Wind Blows... which was fucking DARK. So goddamn bleak. The English can make anything bleak. Seriously, the prologue was supposed to be this peaceful montage of a grandparent visiting the library, the market, and travelling on a rural busline home all before the tragedy of war... but even the prologue makes you feel depressed. And then it only gets worse.
Maybe I'm a naturally sunny personality. But I doubt it.
I still remember the Watership Down animated movie.
I remember crying reading the book as a kid. Blubbering. For hours. The artwork was beautiful and surreal, though, in my illustrated copy. The transmigration of the soul at the end to the place of the primroses was ... beautiful.
So yeah... I mean Watership Down is a children's novel but it was deep, terrible and left you crying. Perfect book for kids to read and realize that war isn't a state, it's a constant companion. Life and its maintenance is a struggle of violence and despair. That death is inevitable and sometimes it's simply better to believe in something afterwards because everything else is fucking tragic.
Perfect lessons for kids. Go watch the movie. It's great!
Go watch When The Wind Blows if you want a reason to hate life and kill yourself. And I don't mean that in that it's bad. A Scanner Darkly is also a brilliant western animated movie that is fairly recent. Also the French animated film Renaissance.
So I don't see the stigma of animated movies/shows being for kids, personally.
(Edit) Animation and comics used to cover a whole lot of topics nobody really wanted to go into details about. Mainly because it was cheaper and more personable to show other imagery than just using stock images of nuclear weapons tests they used to use in all the films.