I'll go one further and say that the real issue can also be the other guests and atmosphere of the event.
Yes.... there can be language, sexual overtones, and of course the blood and guts and horror throughout the event's activities.
BUT... There is also massive amounts of alcohol flowing and extreme crowds. Add in the frightening aspects and the dark, and it can sometimes be a powder keg or a place which may not be the best place to bring a child. The crowds and alcohol can sometimes lead to short tempers, fights, or other incidents which are the reason during HHN the local police are highly visible and have an expanded facility at the hub between the parking decks. You also have a lot more adults who are attending what is obviously a more mature event with lots of alcohol availability who will behave more like they are in a child-free zone than they would in public place which kids could be reasonably expected to be present. [Language, PDA, etc].
I'm personally a firm believer that HHN should be treated as a HARD PG-13/Soft-R type of rating, due to not only the official HHN events, but the overall party atmosphere that the guests can give the place. Some parents and kids could probably feel that their 13 or 14 year old horror junky child can handle the event just fine. While others may feel uneasy letting their 16/17yr old attend. But I do believe that you should know what to expect if you plan on taking your child, and be aware that beyond the straight horror aspects of the houses and scare zones, the child will be exposed to lots of drunk guests, Strong Language, Sexual innuendo, half-naked monsters and performers, PDA, possible violence, and lots of Drunk guests. (Seriously... there is basically a bar every 100ft during the event. I seldom have an empty glass in my hand unless I'm in a house, show, or ride.)