Not to mention, the murder path does not murder the children tieflings
I believe you can find their corpses in "Dragon cave" ... Or at least that is how it was last time i played evil route (patch 3)
Actually, though I haven't tested it yet I think it might depend. If you just attack, you may be able to kill the children. But if you go in, and speak to a specific female tiefling, she states that we got time to seal them away. So if you then go to the gate, and go traitor I think under that circumstance the kids might live. It would be cool if that were true, it would give 2 different options. I am going to try it on my next evil run through. There is a few ways you can do it. I did the same thing in SWTOR, just because your evil does not mean you have to choose every dark choice. I found that pretty dull. I much more enjoyed making my character a little more nuanced, same with the good characters I would play.
But like I said, I think it is far far to early to judge what the evil path is in regards to quality, because we have yet to see the long term repercussions of it. We haven't even seen what the result is at Moonrise tower.