Spoiler alert if you haven't read the story yet.
I first read this as a teenager, and I remember this one line threw me off:
spoiler
“Why you’re one of my babies. You’re one of my own children!”
At the time I thought she meant it literally, and this was a big reveal that she was his mother. Which made me wonder if I had misread the entire story up to that point. It wasn't until years later that the story came up in conversation and someone told me no, that was just a figure of speech. It was not, in fact, history's dumbest twist ending.
To this day I don't think I've ever seen this turn of phrase anywhere else, though. I've re-read it in adulthood and still found it odd. I mean, I get the intention and feel a little silly for misunderstanding it originally, but at the same time, it still seems awkward and abrupt any way I read it. Perhaps I'm just not in tune with Christian symbolism enough to appreciate it.
On a random note, did you ever watch Firefly? One episode features a psychopathic bounty hunter who speaks very calmly and disaffectedly about existential philosophy. It's a creepy episode, and the character always reminds me of The Misfit.