Wehn I was nine or ten I already read my first book with a minor sex implication, you would be surprised how much nine and ten-year-olds, violence is something that actually isn't that dark if it's with swords most of the time. I think if you mention the vague details of it, but cover the action with speech and onomenapeas.
Maybe you fix the age groups because six-year-olds are just starting to read book that have chapter on their own
