The UN Security Council told nations to prosecute those responsible for turning children into killers and soldiers, and for murdering, maiming and raping them during the course of a war.
In its first resolution dedicated to children in war zones, the 15-member body unanimously condemned the "killing and maiming, sexual violence, abduction and forced displacement, recruitment and the use of children in armed conflicts."
The council also said peacekeepers should receive special training on the treatment and protection of children and civilians.
The UN was asked to ensure that all peace agreements and measures devised after the end of a conflict address the issue of children's welfare.
The resolution said all countries were obligated "to prosecute those responsible for grave breaches" of the 1949 Geneva conventions on the protection of civilians in war.
It also called for "days of tranquillity" during conflicts so that immunisation programmes and basic services could be provided for children.
"The sheer magnitude of this problem is something new, is unprecedented," said Mr Olara Otunnu, the UN special representative for children and armed conflict. "It is a worldwide trend. It has spread across the globe," Mr Otunnu said. Some 300,000 boys and girls under 18 years of age, most of them under 15 and some as young as 7, are serving as regular soldiers, guerrilla fighters or porters, cooks, sexual slaves, and even suicide commandos in some 30 countries in conflict.
Over the last decade, wars have killed 2 million children, left 6 million maimed, created 1 million orphans and 12 million refugees.
The heavy toll is mostly the result of civil wars that have escalated since the end of the Cold War in such places as Sierra Leone, Angola, Liberia, Sudan, Kosovo, Sri Lanka, Colombia and Afghanistan.
International treaties set the minimum age for child soldiers at 15 years old but many UN bodies and nations want it raised to 18.
Iraq used the occasion to accuse the US of genocide in keeping stringent UN sanctions in place, thereby endangering the lives of thousands of children.
India's ambassador, Mr Kama lesh Sharma, spoke against young Afghans indoctrinated in Taliban schools and seminaries in Pakistan and then sent home as "cannon fodder".