I marked "pause" for kids ten and under. If you are showing this to a ten-year-old, he or she had better be a VERY mature ten-year-old. This is not Finding Nemo, to say the least. I am sixteen, and I first viewed this film not long after turning sixteen. It moved me to tears. I truly cannot express the horror this movie will invoke in you. It left me very shaky and upset the rest of the day. As Roger Ebert notes, this is a film so powerful it demands a rethinking of animation. It's not your typical Western animated film, or even your typical anime film. It's important to know your kids can take this movie. I'd say if they can handle Bridge to Terabithia they could handle this, but just make absolute sure they are ready--perhaps give them a briefing about WWII and what took place in Japan at the time.
As to the actual movie? I can't say I'm sorry I watched it. The film moves along at a reflective pace, unfeelingly documenting the cruel, tragically brief lives of the two main characters. It often lingers on details, just a character standing in silence or a girl crying on the ground. It doesn't say anything; it doesn't have to. Needless to say, this movie is very upsetting but it is a movie that everyone should see at some point.
On an unrelated note, Setsuko's English voice actor is abysmal, and I could hardly take the annoyance her voice invokes. Next time I will watch it in Japanese with English subtitles.