Children have fought in wars throughout history and into mythic pre-history.
David was not an adult when he slew Goliath. Napoleon's forces were preceded on to the field at Waterloo by drummer boys, who were mown down by English fire.
Yet even in remote antiquity there was seen to be something anomalous and wrong about thrusting children into harm's way.
The ancient Romans seem to have required their soldiers to be at least 16 before sending them into battle.
And although the chaos that followed the departure of colonial powers from Africa and elsewhere has seen large numbers of children all over the world swept up in warfare, children's charity Unicef is not isolated in its efforts to rescue them. Its work rescuing child soldiers in the Central African Republic is supported by a growing body of international law, by successive UN Security Council resolutions and other initiatives.
Is it utopian to imagine that those efforts could one day soon be crowned with success that child soldiering could become just another ugly historical fact, like bubonic plague? "I've wrestled with that question," says Unicef's Pernille Ironside.
The Canadian woman heads the agency's work on child soldiers and spent nearly four years in the Democratic Republic of the Congo coaxing warlords into releasing their youngest troops. Now based in New York, she has led negotiations to secure the freedom of thousands since then.
The involvement of children in the barbarous civil wars in Sierra Leone and Liberia, and the Rwandan genocide during the 1990s, shocked and appalled the world, with their images, as Ironside says, "of children with AK47s and teddy bears on their backs".
Then in 1996, international Mozambican advocate Graca Machel, wife of Nelson Mandela, wrote a report on the impact of armed conflict on children, which galvanised the international community.
The report led to a protocol on child soldiers, which 150 UN member states have now ratified. "That's hugely important in the global scheme," says Ironside, "because each of those member states must implement the terms of the protocol, which stipulates that children cannot be in armed hostilities if they are below the age of 18. They can join the military at an earlier age but they can't be deployed."
The report also led to what she calls "a cascade of measures" that have greatly increased the psychological pressure Unicef can bring to bear on recalcitrant commanders. One of the most important moments in the world's war on child soldiering came last March with the conviction for war crimes of Congolese warlord Thomas Lubanga.
"News of his conviction spread very quickly," Ironside recalls, "and had repercussions with the military commanders we are dealing with in Goma; in eastern Congo they were concerned that the same thing might happen to them."
Despite the vile abuses to which many child soldiers are subjected, Ironside sympathises with the way that entire communities can be caught up in warfare. Some child soldiers are abducted but others join to get revenge on those who killed their parents or just because they have no other means of getting food.
Yet even in places where children identify deeply with the cause for which they have been fighting, Unicef has scored notable successes. One of the most remarkable was Nepal, where thousands of children fought in the civil war on the side of the insurgent Maoists. After years of fruitless negotiation, the Maoists capitulated to Unicef's demands in December 2009 and then required the agency to take responsibility for 2973 liberated child soldiers in little over a month.
"Our message to them was, you can still be politically connected but you cannot be connected militarily. You need to go back to schooling, you have your whole lives in front of you, you can choose to rejoin the army once you are 18. And in fact most of them did want to go back to school or into vocational programmes."