It'd be interesting to make a survival horror game with a Virus that only affects adults, so the survivors (i.e. you) would not only be constantly surrounded by feral mutated adults, but have perfectly normal kids mixed in with the crowd.
I think that'd be a great survival horror game as you would be so hesitant to actually fire on your aggressors for fear of hitting an innocent child that you'd be shitting yourself the entire game. In dark levels you wouldn't know whether those footsteps coming towards you would be infected or children, how in the hell would you find the total lack of compassion to fire indiscriminately? That's about the only way I'd find killing children acceptable, since the only true horror these days is when we are forced to go against our own morality.
Also, the taboo around killing children is because they are naturally weaker than adults, so it's a little unfair to make them the bad guys, even if they're somehow turned feral. While turned adults could be considered to be on equal ground to your character, that's never the case with children. Even the poster game for child cruelty, Bioshock, gave them a big burly protector and the option to save them rather than chop them up to get at their tasty bits.
