Just War
I have to say I am pretty cynical about any construct of a "Just War", especially one that is largely the product of European Culture.
However, I do believe no armed force should "target" civilians. That is not to say there are circumstance where their deaths are largely unavoidable.
I also believe that any man, woman or child, that carries, operates, or directly supports weapons systems should not expect their gender or age to protect them. That is not to say that good judgement and some compassion may not be called for. I don't want anyone killing some 8-year old kid carrying ammunition for his father. - no problem with killing the dad who allows his kid to do that though!