A charity has said most victims of sexual violence in conflict zones are children who are suffering rape and abuse at an appalling rate.
In the worst-affected countries, such as Liberia and Sierra Leone, children made up more than 70% of victims, Save the Children said in a report.
The study contained harrowing stories of children being killed after being raped and of others who were abducted and abused by armed forces and groups.
It also said children as young as two were being attacked by opportunistic predators, including teachers, religious leaders and peacekeepers.
Many survivors were cast out from society after the attacks.
"It is shocking that in conflict zones around the world, children are being raped and abused at such an appalling rate," said Save the Children chief executive Justin Forsyth.
"Sexual violence is one of those hidden horrors of war and the damage it wreaks ruins lives."
The issue will be on the agenda at a meeting of G8 countries' foreign ministers hosted by British Foreign Secretary William Hague in London this week.
Save the Children found more than half of victims of sexual violence in conflict zones were children.
It cited a study in Liberia, still recovering from a civil war that ended a decade ago, which found more than 80% of victims in 2011-12 were younger than 17. Almost all were raped.
In post-conflict Sierra Leone, more than 70% of the sexual violence cases seen by the International Rescue Committee were girls under 18, and more than a fifth of those were under 11.
In Democratic Republic of the Congo, nearly two-thirds of sexual violence cases recorded by the United Nations in 2008 involved children, mostly adolescent girls.