Up to one billion children live in countries or territories affected by armed conflict, with millions of children killed or disabled as a consequence of war and many more in situations of extreme physical and emotional risk. Fifty-million children have been forced to flee their homes by humanitarian disaster and conflict, and experience horrifying levels of trafficking, exploitation and abuse. These children are in already desperate and terrifying situations. They are also vulnerable to being abused by the soldiers and civilian staff sent to protect them. In conflicts and crises across the world, humanitarians and peacekeepers have subjected children to rape, trafficking, violence and abuse, demanding sex for the basics of survival - food, shelter, education and medicine. Too often, children have no way of reporting the abuse, no access to medical or psychosocial care and no recourse to justice. The organizations that fail to protect children continue putting them at risk and the abusers go unpunished. In those most fragile contexts, the opportunity for an abuser to commit crimes with impunity is significantly higher. Thousands of organizations all around the world are doing all they can to protect children, but many more are putting them at risk and there is no single, international, legal framework or justice system in which they can be held accountable. The authors explore how and why these abuses occur and propose a robust and evidence-based solution for safeguarding children in these situations.