Doesn't matter what they were. What matters is the dude's intent. He didn't kill ISIS Fighters in general. He only killed ISIS fighters that were too young to make a decision. The difference there is clear.
In all honesty, most 12 year old American kids don't deserve much better than the muzzies. But they are friggin' 12. 12 year olds don't know shit. By the laws of the universe itself, it could be proven that all 12 year olds are useless drains on humanity and should be gassed with no 2nd thought. But that's not the way to do it. They are 12. Even kids of terrorist's deserve a chance.