Not really a depressing movie... but mk. I'd say Grave of the Fireflies but i'm not sure if it's really a kids movie. So yeah.
I wouldn't call "Grave of the Fireflies" a kids' film just because it's animated. It's like saying "Robot Chicken" is for kids because it has dolls and puppets in it. I don't know why cartoons still have this bad rep in the U.S. for being exclusive to the child demographic, but it hasn't stopped "Family Guy" or "The Simpsons" or "Evangelion" from being watched by adults, eh?
I tried watching "Grave of the Fireflies" a few months' back; I've yet to get past the 30-minute mark before turning it off, simply because I was too bummed to watch the rest of it. I'd have to say that movie's the most depressing movie I've
ever seen, simply because I can't get through it.
As far as kid-friendly films, the most
depressing one I've seen is...I don't know. I'd have to think about
all the kids' movies I've seen in order to give this fair judgment. Plus, I usually don't cry during the depressing parts of a film; I see them as complications that just have to be dealt with. I do, however, cry when everything works out in the end. In that regard, the most
emotional kids' movie I've ever seen would have to be "Homeward Bound: The Incredible Journey"; I was physically fighting to hold back tears when the cat made it out alive after surviving the waterfall and being picked up by the cabin dweller and when I saw the golden retriever limping toward his human at the end.