Is The Boy and the Heron Appropriate for Young Kids?

Please no spoilers in this thread as best you can, though I understand if you need to generally refer to scenes or characters that might be relevant to my question.

My kids are 6 and 4 and love many of the Ghibli movies that are lighter in tone, including Totoro, Kiki's Delivery Service, Pom Poko, and Ponyo. They've also gone for slightly more mature adventure-y ones like Nausicaä and Castle in the Sky.

However, I tried watching Spirited Away and Howl's Moving Castle with the older one at home (maybe a year ago) but in both cases, they were a too intense for her and she wanted to turn them off within 10 or 15 minutes. Now that I think about it, I believe it was Chihiro's parents turning into pigs and Sophie turning old, respectively, that kind of freaked her out.

For those that have seen The Boy and the Heron, what are you thoughts on how appropriate it would be for small children? Is The Boy and the Heron lighter in tone, or does it have some darker elements that might freak them out, especially on the big screen?