There aren’t many of those sites, which means the ones there are great ones! Two of them really shine above the rest:
www.moviemom.com
Reviews of all movies by moms for moms.
http://www.kids-in-mind.com/
I find this site extremely interesting, and it is probably exactly what you are looking for. It does not review the movies based on merit, but on content. It rates movies on three criteria: Sex & nudity, Violence & gore, and profanity, each from one to ten. Here’s the exciting part: Every instance of sex, nudity, violence, and gore is listed as bullet points under their respective categories. And I mean every instance. Also, there is a list of how many instances profanity was uttered, and how many of each profanity type. There is a list of displays of substance abuse, and convenient discussion topics. Even more convenient is at the end of each review, the message is listed.
Both of these sites have reviews for almost every movie that comes out. I hope this helped!
-Dan