They did see a civilian witchhunt before, a few months before the war ended.
They were five at the time, so they do not remember much; especially because their mother made sure they did not get to actually see... but they did smell the smoke and heard a few screams.
As it turned out, that girl was no Magical Girl.
That said, they do not know this kind of practice is long since banned; only the military takes care of Magical Girls at this point... by shooting or tranquilising them, whichever works.
They do not think much about it... first because they were no Magical Girls, now because they are children and there are a lot of other things to take up their thoughts and curiousity.