Khadr is not a child soldier.  He is a terrorist.  He was not in any military, or representing Canada.  He did not enlist, and was not supplied by the Canadian military.  He was a lone wolf terrorist.

In 2017, if someone whose family is from Syria were to leave Canada as a 15 year old to throw grenades at US soldiers in Syria, he would be called a terrorist.  For some reason, Khadr is being called a "child soldier".  That is an insult to children who are forced to be soldiers, at the threat of death if they don't fight.