...8-year-old who loves to watch me play Team Fortress 2...
...Same one who watches The Walking Dead with us...
Something is rotten in the state of Denmark...
I know how it feels to know a pretty cool little kid. I know one myself, although he's a bit less intellectually oriented than you make your sister out to be.
I was quite the same back in the day. Viscera, ghosts, eldritch horrors, and the like; nada. Being the goody-two-shoes kind I was (though my lack of reaction would make others think otherwise about me), cursing and nudity is involved, and I mute it and shut my eyes; to the point it was force of habit until adulthood (yes, even when I needed to curse, myself, I kept myself censored from cursing. At least I kept my wit sharp, in lieu of the common verbal curse collage.).
Forget the fact that I've seen creatures and people explode and such, along with terrors that are far scarier than things I was once scared of (Freddy Kreuger was scary; and then I learned of elder gods on my first playthrough of Quake and Doom, and learned these things can be killed. No longer scary), but God help me if I am vulgar, or am aware of the naked body; especially a female body (I suppose it was fear of me becoming a pervert or something in the future; oddly enough, male nudity was no problem for anyone, because naked people are funny, but naked woman appears, and now it's censored full-stop by anyone and everyone, even into my late-teens. By this era, who isn't perverted by now? I'm sorry to even need to ask that. In fact, I'm ashamed I even need to ask that these days. Porn is inevitable; so much so, I've practically built up an immunity to it. I'd cover my eyes or look away, out of courtesy, but if anyone used it (nudity and the like) for seduction on me (unlikely as it sounds), I'd have to ask if it's part of a prank show or something, and look for the hidden camera.). I was raised weird, I'll admit; the priorities weren't quite there. Witnessing violence is fine, but nudity isn't.
EDIT:
Funny story. Kinda reminds me of a minor incident after working one night at the local tavern. I was on a roll playing an arcade game (bowling, I think), and I swear, a girl that passed by me a few times that noticed me playing the game (I was playing maybe the third time in a row, attempting to beat 200, and hit the high-score board) must've tried to flash me to draw my attention in order to mess me up. Fortunately, I was buzzed and too focused on my game to be distracted by such a thing. And even so, if they really wanted to distract me, you cheer for me instead of trying to distract me with your body. I hate being cheered for. It's lame as hell, and I intentionally screw up in order to disappoint the fans so they stop bugging me. BTW, even if I were to approach them later on, in case they were trying to get my attention, I would assume they only wanted to troll me and mess my game up (maybe even do the rude thing, and call me a pervert for noticing, out loud, to humiliate me for kicks, if I even approached them later on. Knowing people in my town, and my vulnerability to being a target for unnecessary bullcrap (I am always a popular target/mark), this is the majority conclusion. They wouldn't be doing that to attract me; they'd only do that to distract me.). If they truly took interest in me, they'd have stuck around until I finished playing (which I was on the last frames, at the time), and hell; break the mold for once, and approach me instead, or something. Her loss.