Save the Children on Wednesday urged action after releasing a report claiming that most rape and sexual abuse victims in many of the world's conflict zones were children.
The report, entitled "Crimes Against Children", cited data and testimonies from countries including Colombia, Liberia and the Democratic Republic of Congo.
The charity warned that programmes to help children who are victims of sexual crimes in war zones and post-conflict regions were massively underfunded.
"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's Chief Executive Justin Forsyth.
"Sexual violence is one of the hidden horrors of war and the damage it wreaks ruins lives.
"Even if they recover from the physical effects of their experiences, many victims carry the psychological scars of their ordeal for the rest of their lives, and are often cast out from society. Despite all this, there are huge gaps in funding for the work needed to protect children from these atrocious crimes and to respond to their needs," he added.
The issue will be on the agenda of the meeting of G8 foreign ministers this week.
The report highlighted a study in post-civil war Liberia which found that 83 percent of victims of gender-related violence in 2011-12 were under the age of 17.
Another investigation in post-conflict Sierra Leone found that more than 70 percent of sexual violence cases were committed against girls under 18.