Ding! Ding! Ding! We have a winner! Enemy is enemy. If their mission is to kill or impede your mission, they are then enemy and are a legitimate target - period.
BUT- since we HAVE arrested such “enemy combatants”, who should have jurisdiction? Canada sure isn’t going to do anything about this punk kid. Afghanistan isn’t going to do anything. Yet how could this possibly fit into civilian law in the US?
What do you do with the ones who surrender? Or the ones you capture intentionally to gain INTEL?