Ironically, perhaps the best description of Omar Khadr's status as a child soldier was stated by the terrorists themselves, in a biograpphy of Omar Khadr's father, Ahmed Said Khadr, in the "Book of 120 Martyrs in Afghanistan", posted online at the Al-Fajr media centre, al-Qaeda's online news service. The CBC website states that the biography praises Ahmed Said Khadr for "tossing his little child in the furnace of the battle."
Under the Optional Protocol to the Convention on the Rights of the Child on the involvement of children in armed conflict, which was adopted and signed in 2002, the use of anyone under the age of 18 in combat is illegal under international law. National armed forces are permitted to recruit individuals below the age of 18, but are strictly forbidden from deploying them into combat. Non-state actors and guerrilla forces are forbidden from recruiting anyone under the age of 18 for any purpose. (Military use of children - Wikipedia)
Indeed, do we consider "a little child tossed in the furnace of the battle by his father" a terrorist or a victim. International law requires that we consider child soldiers to be victims not warriors.