Truth be told, murdering human beings in video games generally has about the same emotional/moral impact for me as squishing a spider. I don't see why uncharacterized dead babies should make much difference. I had no issue slaughtering them in Doom 3 or Dead Space, I just shot em and moved onto my next objective, fully aware that what I just killed was simply a means to an end (read: survival).
In fact, the only times I actually question what I'm killing in a game is when said victim has been characterized to the point where I actually start wondering if what I'm doing is morally acceptable, both in my mind and the context of the game universe. Mass Effect did a fantastic job of this. Hell, I spent a good two minutes debating the fates of some of the characters from Grand Theft Auto 4. However, if those characters were ambivalently evil or weren't characterized, I would have no issue pulling the trigger immediately.
I always keep in my mind that all I'm doing is playing a video game. It has no impact on my life past the time I spend playing it, and I know when to separate fantasy from reality. Murdering dead babies in a video game doesn't strike me as morally unjust (seeing as they are nothing more than pixels), but rather a video game "enemy" whose very purpose for existing is to make the player uncomfortable.