I saw this with a dd(10) and ds(7). I was totally enchanted - visually it is absolutely stunning.
It does take a long time to 'get going', which in my view is a great antidote to the instant gratification so prevalent these days.
There are some 'strong' scenes which really engage the emotions, but the girl gains wisdom in the end, and ultimately no one dies.
From someone who is a sucker for gorgeous visuals and a simply-told story, I loved it, and my dcs liked it also, although my dd did say it was quite sad.
I don't want to give the plot away, such as it is, but I think it's good for opening up discussion, if that's what you want. However, if your dcs will be happier with a film that's purely 'feel-good', it's probably not for them.