Robin Hood Prince of Thieves contains plently of sex, violence, and language, making the movie not appropriate for anyone under the ages of 12 or 13 (it depends on your child). The whole movie is violent, and there are several frightening bits. Language like "blimey!" is frequent, until we get closer to the end and people start saying real bad words. The sexual content comes from, surprisingly, not Robin and Marain, but the Sheriff and Marian. At the end of the film, the Sheriff attempts to rape Marian in order to impregnate her, for, once he has a child of royal blood, he will be king. He doesn't actually suceed (the moment is interrupted by Robin crashes through a window), but he gets close enough.
So, I'll leave it up to you on this one. But, in all honesty, you should probably watch this movie before deciding, because parental reviews really can't tell you a lot about this movie. You'll like it, but maybe your kids should wait awhile.