Not a movie, rather a show, and also not complete yet, but The Dragon Prince on Netflix is pretty good. The titular prince is a dragon, but there are human princes as well, with one becoming a king actually pretty early on. And King Ezran absolutely tries to bring people together peacefully and with honorable intentions, though there is some action/fighting as well. Caveat, while it is a kids show, it might be thematically better for kids a bit older than 6, as some of the themes can be a bit dark for a kids show, but I'd just recommend you watch a couple eps yourself before showing it to the kiddo and decide for yourself if it's appropriate.
Also, someone else mentioned Avatar: The Last Airbender in this thread, which is also excellent, and if you happen to be familiar with that show, it has a lot of similiarities and it's some of the same writers and directors of that show.