France's foreign minister has warned that the use of child soldiers is a time bomb that threatens stability and growth in Africa and beyond.
The use of children in combat is now defined as a war crime
Philippe Douste-Blazy told a Paris conference child soldiers were "lost children, lost for peace and lost for the development of their countries."
An estimated 250,000 child soldiers are now fighting in wars, mostly in Africa.
Delegates heard a former child soldier tell of his experiences on the frontline in Sierra Leone.
Ishmael Beah, who fought for almost two years, described shooting someone as being "as easy as drinking a glass of water".
The former child soldier, now 26, was barely 13 when recruited to fight in an armed faction in Sierra Leone.
"It is the most difficult thing to regain your humanity. I'm living proof that it is possible," he said.
UN WATCHLIST FOR CHILD SOLDIERS
Democratic Republic of Congo
The two-day conference, hosted by the UN children's agency and the French government, will seek to get countries to sign up to a new framework of action known as the Paris Principles.
These aim to ensure countries work harder to release children from conflict and reintegrate them into normal life.
Mr Douste-Blazy said that countries that recruited children to fight should no longer be allowed to "slip through the net".
Mr Beah said that a failure to follow through on rehabilitation programmes left children at risk becoming mercenaries and fuelling further conflicts.
"They know how to use a gun. And there is a conflict next door offering $100 a day and all-you-can-loot, and they will go back to that," he said.
Several countries are under special scrutiny by the UN over child soldiers and there has been growing concern over the use of child soldiers in the troubled Darfur region of Sudan.
Since 2002, the International Criminal Court has defined the use of children in combat as a war crime.
Last week, it announced it was opening its first trial - against a Congolese militiaman Thomas Lubanga, accused of recruiting child soldiers during the Democratic Republic of Congo's civil war between 1998 and 2003.