Except the gameplay is completely different from Left 4 Dead, and so is the visual style, and for all we know, there are no children actually in the game, but A+ generalization and assumptions there, genius.
Yes, there's a dead kid in the trailer, and I think that's awesome. They crossed the line to show that even children are victims in a situation like this, and to emphasize your hopelessness. The game is made out to be extremely bleak and horrifying, so the trailer did it's job well. There are not "nasty people" writing it, haven't you ever seen Dawn of the Dead? Children are an unfortunate casualty in a horrifying scenario like a plague or outbreak. Really, I think you need to mature up and actually try to understand it without your ignorant biases.
Also, there is an extremely good chance that there won't be kids in the game. ESRB won't give out ratings to any games where children are murdered (which is why you never see kids in games like GTAIV). Bioshock got through because you don't actually SEE what happens to the little sisters when you do something bad, it's only inferred.
