When i got to little lamp light, i met with some annoying kids, i got mad (yeah i got short fuze) and started shotting them all,
but then i discovered (in the previous playthrough i never tried to kill anybody that hadn't attacked me first - so i never have tried kill kids, but now - im an evil person :mohawk: )
that they are immune to my Plasma Rifle! WTF!?
WHY I CANT KILL THOSE LITTLE KIDS?

You are not able to kill kids in Fallout 3, likewise you are not allowed to discuss this topic on our forums.

From the Forum Rules: Likewise, discussion of killing children is not permitted as it is classed as http://www.gamesas.com/bgsforums/index.php?showtopic=644280, neither is it a feature of Bethesda Softworks games.