ya i know you cant kill kids he might of said it has a example. and he might of made a mistake you can kill evryone but one person, maybe there is only one kid...
I believe it's already been said that there is more than one child in the game. And it's also been said that you can't kill children, the "You can kill every person except one" thing only applies to advlts, from my understanding. Now who is this person? I don't know, I'd guess someone important, as there's certainly no reason to make a random wastelander unkillable if you want to give the player as much freedom as possible in terms of who you kill, but who, exactly, did Obsidian decide is important enough to be impossible to kill? Only time will tell.
I recall in one interview (I don't remember where I saw it, so I can't link to it.) someone asked if you could kill children, to which I recall the answer was no, but there's not that many in the game.