I asked myself, what if a child finds this site through a search for Harry Potter and sees the question about the beheaded wife of the detective in Se7en. How should we handle this?
The Terms of Service prohibits usage of this site for users below the age of 13.
The content of all Stack Exchange sites must be "work safe." That means no explicit imagery or language is allowed on the sites. Beyond that, the ideas or themes expressed are not expected to be watered down to be consumed by an 8-year old. That's true of almost any literature, television program, radio program, or news outlet anywhere. Finding age-appropriate content for children — whether that is in literature, television, or web sites — is the responsibility of the parent.
No offense, but this is is the Internet. It isn't the responsibility of SE communities to filter our content to be age-appropriate, it's the responsibility of parents to ensure children use the Internet in an age-appropriate way.
That said, there is a line of appropriateness (that I don't believe has been crossed yet). Text descriptions of the events of Se7en are well behind that line (in my opinion at least); stills from that movie could definitely cross it, depending on the scene. Either way, I definitely don't believe we should be policing content based on age-appropriateness (just for appropriateness to the community as a whole).