There is also the issue of the lack of privacy. Even if you could ensure that such material is blocked at a child's seat, what about the person next to a kid? Do you bar them from watching it as well? How do you deal with any potential conflict? I remember a flight where some guy was watching Monster on his computer. Good for him, but I could clearly see it (again not a problem), but it isn't appropriate viewing for a child, and I didn't see him take any measures to ensure a kid couldn't see it. Editing the content helps prevent any such issue.