It just dawned on me how fucked up it is to have you killing a baby (Arianna's) in the game, and I wonder if the reason why they both die together is so if you stab only the baby, From can excuse it by saying you missed and stabbed both, and that it's not possible to target and kill the baby.
When the game was being submitted for a rating to CERO in Japan, they initially were told that the game would get a Z rating, but that's a big problem because you 1) can't advertise on TV and 2) can't make display cases in electronic stores, so it really affects sales. The reason they were given it'd be Z is that the player can kill innocents. Sony told them that they aren't innocent, they're enemies, and they resubmitted for a rating. I think it might have been referring to the newborn baby you kill.
I know this because my friend worked on the box art and told me that this all went down the week of going gold, so he had to submit two pieces of artwork to the printer, one in the case of Z rating and one in case they lowered the rating to D. The day they'd find out about the new rating was literally the day of printing. As it happens, it was lowered to D in the end.