My hubby and I bought the Nicholas Cages movie "Ghost Rider". We ended up seeing it several times when the kids were not home. One day I went into the 3 year olds bedroom because he was being too quiet. He had put the movie in the DVD player and was sitting watching it. He suddenly had a favorite movie.
I know, I'm a horrible parenting figure, but he had already seen it so the damage was done. It is the ONLY movie of this kind that is in his reach now. He is 4 now and has access to lots of other movies and has stopped wanting it.
I think the ratings are there for a purpose. One time we went to see the movie "A Few Good Men" which was rated "R". The ticket person was selling tickets to younger teens. I asked the ones I knew if their parents knew what they were seeing and they said yes, of course I asked the parents later too. But the ticket guy told me that the movie should have been rated PG13 but Jack Nicholson, Tom Hanks, and Keifer Sutherland thought the movie would do better if rated "R". The ticket guy also told me it only had brief flashes of violence, was mostly courtroom scenes, and had really bad language. So that's why they were letting younger teens in w/o parents.
I think if you want to decide if your child is going to see this movie then you should rent it and watch it when they are not around and then decide. As for me, PG13 is as far as I am willing to push the boundaries with a 7 year old and that is only if it is an appropriate movie for her to see, such as no love scenes where there is extended kissing or too close of contact. No sneaking out or other unwanted behavior.
So not too many would be allowed if any. When she is older she won't be watching ANY horror movies at my house because I don't want to see them for any reason. I don't want those images in my head.
I am a wuss. My hubby is a huge Heinlein fan. He has all of his books and some are signed by the author. He wanted to go see "Stormship Troopers" to see how Hollywood had interpreted the novel. I sat beside him with my thumbs in my ears and my fingers over my eyes. Seriously did. He laughed at me but it was too graphic for me. So, for me, if I can't watch it it isn't going to be watched in my house.