Child soldiers at an ethnic Hema militia camp near Bunia
Although the war finished in 2003, hundreds of children die every day from hunger, disease and violence. Children are still being abducted, raped and recruited as soldiers by the armed forces and rebel groups.
Armed groups enlisted 25,000 children during the war - UNICEF.
Girls are raped and forced to become sex slaves to fighters.
U.N. peacekeepers stand accused of sexually exploiting children, giving them food or money for sex.
One in five children dies before their fifth birthday.
Child labour is likely to become an increasing problem as investors rush to exploit Congo's vast resources.
"I don't want to go back to the army. I would like to have some goats for stock breeding, but I can't go home: I'm sure the soldiers will come and take me again." Izaak, 15
Some 1.8 million children have been affected by a three-year conflict in Darfur, according to the U.N. Children's Fund (UNICEF), where they risk being recruited to fight and are especially vulnerable to disease and malnutrition.
"It is a traumatised population and you can see it in the children's faces," said Hollywood actress and UNICEF goodwill ambassador Mia Farrow, who last month visited camps for some of the 2.5 million displaced by Darfur's war.
"Everyone has lost family, seen villages burn, seen relatives raped, been raped."
U.N. High Commissioner for Refugees Antonio Guterres - who selected Congo, Uganda and the Sudan/Chad border, where some 200,000 refugees from Darfur eke out an existence - pointed to the physical and psychological consequences of living in crowded, underfunded camps "which are not conducive for a healthy child development".
In southern Sudan, children also suffer the effects of low-level violence, poverty and a lack of basic services. The region is struggling to recover from a 21-year civil war with the north that killed 2 million people, as 600,000 refugees forced to flee the country trickle home.
AlertNet, a humanitarian news website run by Reuters Foundation, asked 112 aid experts and journalists to highlight the world's most dangerous places for children.
After Sudan, they chose northern Uganda, Democratic Republic of Congo, Iraq, Somalia, India, the Palestinian territories, Afghanistan, Chechnya and Myanmar - with the top three clearly ahead.
More than 2 million children worldwide have died as a direct result of armed conflict in the past decade, and about 20 million have been forced to flee their homes, according to UNICEF. More than a million have been orphaned or separated from their families.