With regards to the “civilians” conversation,
We need to make a differentiation between Criminal Justice, and War. In Criminal Justice, especially Jewish Criminal Justice, you can only convict someone if you have certain proof that they committed a transgression. You need two witnesses, and a warning, and a minor can not be liable.
In War, your priority is to protect your people from attack, or to conquer an enemy. Even Western armies will kill a six year old child if he points a gun at the soldiers. In fact, Western inspired international law is much more lenient that we imagine, and most claims of “war crimes” are not. As Jews we must follow Jewish law in warfare, just like we follow Jewish law in eating, Jewish law in marriage, and Jewish law in civil disputes.