Gamasutra has a well thought out, thought provoking response:

http://www.gamasutra.com/php-bin/news_index.php?story=20908

I agree with Simon Parkin over Emil on this. Children are in the world. They should be killable. If you didn't want us killing children? Don't put them in the game at all!

So it's OK to give kids a potty mouth but we can't kill them like we can anything and everything else in the game? Isn't that a contradiction?

You aren't selling Fallout 3: Teaching Morals and Values Edition here; you're selling a game series that in the past allowed these types of questionable actions to take place and the repercussions were HARSH. I realize that it was also 10 yrs ago and Fallout didn't need the ESRB's golden touch to be released, but trying to paint "violence on children" as "gratuitous," in a game that revels in over the top, "comedic" violence is a contradiction.

I would have preferred "ESRB said no" over this "imposing morals in a game where NO MORALS ARE NEEDED" response.

Maybe you can add DLC that will be a side quest of just child killing? Why can't I use them to find all the land mines in the mine field? THAT is something I'd pay for, especially since the children I've met thus far in the game are deserving that job.

EDIT- Postal. That was a game I loved for it's gratuity. You could mercilessly kill anyone and everyone... except children. I ALWAYS hated that fact. You could put them in a custom level you've built, WITH guns. If you did this, you were signing your death warrant as children are unkillable and invincible. Not being able to kill children in Postal, when you could stand over someone begging you not to kill them and blow them away, made the premise of the game less stable and less realized IMO. Same goes for Fallout 3.