I don't quite understand the hostility on this one. And to be clear, yes I think parents do have a responsiblity to guard their children from being exposed to illicit sex acts.
And yes my SD listened to lilicit sex acts at her mother's house and it had a harmful affect on her. It was something that the first GAL was very concerned about.
My SD most likely molested her younder male sibling and touched little boys private parts she went to school with, mounted a little boy on the playground when she was in first grade and touched the private parts of adult men in her family for a time.
Her counselors, GAL and us all thought that she was molested. She never told anyone that she was. If she really wasn't, then the only logical explanation as to this avenue of acting out is most likely the illicit sex acts she listened too.
Yes parents should take protective measures to guard their children from listening to and viewing sex acts. If they don't I do see this as a serious defect in their parenting skills.