I agree with Portia, that it depends upon the child.
Beyond that, it may also depend upon the conversations which the parent is prepared to have with the child, and the messages which the parent wishes to communicate... what do you want your child to have as his take-away after watching this movie?
While I'd not recommend watching in a movie theater, with "Hacksaw Ridge" coming out on DVD this month it may be fine to watch at home... where the image is smaller, you can control the volume, you can stop/pause to have a conversation, and you can also fast-forward if need be.
