Personal Opinion

Which parts?

It gets pretty intense towards the end, but unless you have a very sensitive 6 year old, you're probably fine. Some exposure to "mild movie peril" isn't a bad thing anyhow at that age to wean them off pre-school TV. Bear in mind also that to a child of that age, a film like Moana is a full blown epic comparable to Lord of the Rings, so as the parent you can savour her experience of it.

My similarly aged girl said she didn't like the scary bits but thought that Moana was very brave, and now walks around singing some of the songs, so it's hardly traumatising. She also gave a standing ovation at the end of the movie, so it clearly had a big impact that would probably have been diminished if she were a few years older.

I was exposed to demon boobies at 8 because of the re-release of Fantasia. I turned out fine.

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While I can't really think of anything specifically that would be questionable for children under 10, if you do believe so, keep in mind the movie is rated PG instead of G, and that's what you are there for. If you believe something is too intense or inappropriate for your young child, you can shelter them from that.

For what its worth, my friends took their 3 (well, she turned 4 today, so almost 4) year old daughter to see it, and didn't mention her being overly scared or anything at the movie, or thinking anything in it was inappropriate for her.