I agree with that EandC. Oftentimes both girls are affected by movies where you can take a not so subtle social commentary and easily extrapolate into a very real and scary possible scenario. I'm so sorry DS got upset and I can see why he did.
The strange thing for me is I got so caught up in the artistic beauty of the animation, I was enjoying it so much on that level I wasn't paying as much attention to the thematic aspects of the story.
Spoiler alert:
About half way through I remember looking around the theatre and giggling about the fact that everyone seemed to be enjoying a movie that for an hour had literally no dialogue!
I would definately carefully consider taking a child that has the capacity to internalize that "mild peril" that those animated movies are so famous for.