I walked out on a mainstream movie 10 or 15 years ago that had Laura Dern in bed with a young boy--can't remember the name of it. (Might even have her name wrong!)
They finally came out in the open on behalf of "kiddie porn", which you really have to assume is the favorite form of visual material for all ACLU members (as a consequence of this movie)
The film won the 1979 Academy Award for Best Foreign Language Film. It includes one scene that suggests, but doesn't actually depict, an oral sex act between the boy, aged 6 to 7, and a teenage girl.