Regular kids can be bad enough, but tieflings literally have infernal devil blood in them - that’s to explain why they’re so nasty.
As to why there’s no option to murder them in a game that markets itself as big on freedom of choice - I don’t know.
Personally I don’t care, but I wouldn’t mind in the slightest if there was such an option. Suitable course of action if you wanna RP an evil alignment. But i guess lines have to be drawn.