Parents: have your kids been affected by age-inappropriate content?

I was having a conversation with one of my coworkers who mentioned that her child showed a fascination with scary, Halloween-type stuff starting around age 6. She and her husband had a hard time with whether they should let him enjoy it or limit it. They weren't sure whether to let him read scary books or watch spooky stuff on YouTube, particularly because it's the type of content that can very easily be age-inappropriate--especially for a 6 year old. Nevertheless, it was relatively easy for them to keep it to stuff like Jack-o-Lanterns and black cats since he was so young.

The boy is now older but has retained his interest, and the parents are still struggling with decisions about allowable content, especially because he is starting to age into books and movies that deal with much darker stuff, particularly ideas about death/violence.

I'm not a parent, but I am a teacher, and I have to admit that I'm uncomfortable with some of the stuff my students are exposed to. Over the years I've heard students as young as twelve discuss horror movies like the Saw series or The Human Centipede. I've had middle school students bring books like Gone Girl and 50 Shades of Gray to class. On one hand, I think kids are resilient, and I think a lot of the more difficult or disturbing stuff doesn't quite land for them because they don't really have a context into which to put it yet. I also believe that fictional media is a mostly safe way for us to explore troubling or disturbing ideas.

On the other hand, I think the internet has caused our children to grow up a lot faster than they used to, as they are exposed to mature content (whether intentionally or accidentally) from a very early age. When I was growing up the worst I could do was check out a slightly-risqué book from the school library and hope my parents never found it in my backpack. Now kids are watching violent (often real-world) and pornographic content starting as young as elementary school. Nothing can make your heart sink quite like sixth graders talking excitedly over lunch about a video of a real person getting crushed to death.

What I genuinely don't know is if this has any negative developmental effect. Am I just clutching my pearls here? I'd love to hear some parents talk about how they've handled the decision of what's right for their kids and whether they've had fallout from their kids consuming content that's not appropriate for them.