Anyone who knows about kids' movies knows how popular princess movies are, especially Disney princesses. My child is six and absolutely loves them too. My child also loves princes and kings, but I'm having a hard time finding anything that features a character as easily beloved as Elsa or Moana for example. Even worse, a lot of the times male characters are just antagonists or at least stand in the way of the princess. I'd love to see a movie with a young prince who isn't evil or dumb (as a joke) that kids can relate to. I think it also be cool if there was singing or magic or anything mystical. My kid kind of likes Shrek but I was hoping to find one about a human prince. The protagonist in the movie The Lorax is a young boy on a good mission, and we like that movie too, but we're just looking for something bigger. I'm not looking for a movie that's primarily fighting, a little is okay, but I'd really prefer if the main focus was some honorable endeavor. Am I just missing the prince movies, or are they all about princesses instead?
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.