But killing kids has been around for awhile. Ultima V, Fallout 1 and 2, Crusader Kings, The Witcher, Bloodbourne etc...
It's obviously deeply disturbing but the line has been crossed already.
It would probably cause issues in a number of countries though. I remember how I had to specifically get a foreign version of Fallout 1, because all the children in Shady Sands were invulnerable in the German version.
Temple of Elemental Evil even had all children removed, which was utterly hilarious as dialog wasn't adjusted and at times refered to having met someone's kids.