I don't think anyone has so succinctly described what's so terrifying about encountering kids as John Mulaney in his stand-up special, New In Town:
Thirteen-year-olds are the meanest people in the world. They terrify me to this day, because 8th graders will make fun of you but in an accurate way. They will get to the thing that you don't like about you. They don't even have to look at you for long. They'll just be like, 'Ha, ha, ha, ha, hey, look at that high wasted man. He got feminine hips.' And I'm like, 'No! That's the thing I'm sensitive about!'
And that's it - kids are honest and either don't realize they're being mean or DO realize they're being mean but know they can get away with it because they haven't really figured out the whole "empathy" thing yet. And that's why this r/AskReddit thread of the most brutally honest things children have said to people leaves us with such fear - next time, it could be YOU that a kid is cutting to the core of.