How are trained terrorist children like the old Hitler Youth?

The Taliban, Al Qaeda, ISIS and so many other terrorist groups are recruiting and training younger and younger children to fight wars to the death. Can a child under 7 even have the capacity to think independently about the reasons for fighting? I don't believe so. They fight because mom and dad told them to. That's all they know. This isn't a new concept though. I think of historical events like the Children's Crusade. I think of Hitler Youth. How do the modern insurgent terrorist-trained children in Southwest Asia compare to the Hitler Youth? This makes me want to go read "Lord of the Flies" again.