Nearly 60 nations have signed an accord pledging to prevent the use of child soldiers and disarm underage fighters.
Former child soldier Ishmael Beah appealed to delegates
Although carrying no legal weight, the agreement was hailed as a major step to address the continued use of soldiers under the age of 18.
An estimated 250,000 child soldiers are now fighting in wars, mostly in Africa.
The accord aiming to make states work harder to free children from conflict and reintegrate them into normal life came at the end of a Paris conference.
Known as the "Paris Principles", the accord was signed by 58 states, including 10 countries where the UN believes child soldiers are still used.
They include Chad, the Democratic Republic of Congo, Sudan and Uganda.
Two other states named on a UN list - Burma and the Philippines - did not take part in the Paris meeting.
'More than words'
The agreement was signed at a conference on the issue held in the French capital and organised by UN children's agency, Unicef and the French foreign ministry.
States should tackle reasons why children join armed groups
No amnesty for those who commit crimes against children
Child soldiers who commit crimes are victims not criminals
Countries must to strive to prevent, protect and reintegrate children
The needs of girl soldiers must be addressed
Efforts must be made to reunite scattered families
Countries will be obliged to find child soldiers and help them leave armed groups as well as punishing those who recruit underage combatants.
France's Foreign Minister Philippe Douste-Blazy said the agreement was far more than merely "good words."
"It is a text that will have a great political value," he said.
According to Unicef, children in conflicts are often used as messengers, spies and sexual slaves, as well as soldiers.
Delegates heard an emotional appeal from a former child soldier, Ishmael Beal, who fought from the age of 13 in Sierra Leone's civil war.
"No-one is born violent. No child in Africa, Latin America or Asia wants to be part of war," he said.