A legacy of the Irish Civil War , later to have a major impact on Northern Ireland, was the survival of a marginalised remnant of the Irish Republican Army . It was proscribed on both sides of the new Irish border , and remained ideologically committed to overthrowing both the Northern Ireland and the Free State governments by force of arms to unify Ireland. The government of Northern Ireland passed the Civil Authorities (Special Powers) Act (Northern Ireland) 1922 ; this gave sweeping powers to the government and police to do virtually anything seen as necessary to re-establish or preserve law and order. The Act continued to be used against nationalists long after the violence of this period had come to an end. 
Under the Convention on the Rights of the Child on the involvement of children in armed conflict adopted by the UN General Assembly in May 2000, the compulsory minimum age for combatants is 18.
Follow The New York Times Opinion section on Facebook and Twitter , and sign up for the Opinion Today newsletter .