There's plenty of stuff on Netflix that while not strictly pornography, is really R-rated (nudity, sex scenes, etc.). There's also a few documentaries that cover sex-related topics, foreign films that are listed as "unrated", etc.
Content filtering on Netflix is lacking. You can set restrictions on the entire account, but you can't filter by profile (yet). The only real solution for now is to get a separate Netflix account for the youngsters and lock it down.