I'd have no problem killing a sociopathic child. While one would have to consider a lot of things in order to determine if a child was a sociopath, once that determination was made, hasta la bye bye.
As far as collateral damage, perhaps our enemies need to think things through before they attack the US. Funny thing, the "liberals" didn't have one care about carpet bombing Germany and killing innocent civilians and their children. The atomic bombs that were dropped on Japan didn't meet much opposition here in the US, either until a couple or more decades afterwards. Then there was the fire bombing of Japan. Again, little or no opposition.