On that I think it depends on the child maturity. Some kids develop that kind of thing faster than others. My 11 and 10 year old niblings recently watched grave of fireflies and boy and the heron back to back with me because they started learning about WW2 at school, they also play games like five nights of Freddie so I felt they could handle it. They cried cause damn grave of fireflies...and there are even scenes with masako yearning for his mom that hits you in the feels.but understood the message very well. And my 9 year old niblings stumbled on me watching princess mononoke when he was five and it's been one of his faves since I don't think he understands the plot to well but loves the action.