How long and how far do you go with that justification? Does it work the other way too? Are "their" actions justified forever because of something wrong that was done to them? Can anyone in the world do to you anything and everything forever if they were ever wronged by someone born in the same general geographic area as you?
Whenever you find yourself defending any genocide, under any excuse, defending the killing of innocent children because some other guys from the same general area also killed people, you are the bigger problem and no amount of fresh accounts justifying it makes you better.
That in itself is an abhorrent position and I am disgusted at anyone who takes it.
And further extrapolation as you edited it, if a child has a gun pointing at your head and has been trained to fire it at you, which is exactly what they have been doing, then they are legally combatants. But it makes a good statistical and PR job which is just as abhorrent. Legally and statistically speakingh, children... https://www.youtube.com/watch?v=cD2FezhJgqA
I would not do this to MY children.