PALORINYA, Uganda — On a pale dirt road in the Palorinya refugee camp in northern Uganda, Raida Ijo clung to her 16-year-old son, Charles Abu. They sobbed quietly into each other’s shoulder. They had been separated for 19 months, since the day that fighting broke out between rebels and government troops in their village in South Sudan.

Charles was halfway through a math class in their village, Andasire, in South Sudan’s Central Equatoria state, when the shooting started. He ran for the bush, and after a sleepless night in hiding, set off for the Ugandan border with his younger brother, Seme, 14.

Their mother, Mrs. Ijo, feeling unwell, had checked herself into a hospital that morning. The boys knew that to try to find her would be too dangerous.