More than one million children have fled South Sudan's civil war amid the world's fastest growing refugee crisis, two United Nations agencies said.
Another one million South Sudanese children are displaced within the country, having fled their homes due to the civil war, according to the UN's child and refugee agencies.
"The future of a generation is truly on the brink," said Leila Pakkala, Unicef's regional director for eastern and southern Africa.
"The horrifying fact that nearly one in five children in South Sudan has been forced to flee their home illustrates how devastating this conflict has been for the country's most vulnerable."
The civil war has worsened South Sudan's ethnic divisions and UN officials have said parts of the country are experiencing ethnic cleansing and are at risk of genocide.
Roughly 62% of refugees from South Sudan are children, according to the UN statement, and more than 75,000 children are alone or without their families. Roughly 1.8 million people have fled South Sudan in total.
"No refugee crisis today worries me more than South Sudan," said Valentin Tapsoba, the UNHCR's Africa bureau director. "That refugee children are becoming the defining face of this emergency is incredibly troubling."
For children still living in South Sudan, the situation is still grim. Nearly three quarters of children are out of school, according to the UN statement, which is the highest out-of-school population in the world.
An official famine was declared in two counties of South Sudan in February, and hundreds of thousands of children are at risk of starvation in the absence of food aid, according to the UN.
More than one thousand children have been killed or wounded in the East African nation's civil war. Both sides have pledged not to recruit child soldiers, but have ignored their promises. A UN official said that opposition groups are recruiting inside UN displacement sites.
South Sudan's civil war began in December 2013 and has killed tens of thousands of people.
South Sudan's government forces "continue to target civilians in violation of the law of armed conflict", the United States, United Kingdom, Norway and European Union said on Monday, one of the most critical statements by foreign governments against the East African nation as it experiences a sharp rise in ethnic attacks.
"Large government offensives in Yuai, Waat, Tonga and Kodok have resulted in even more tragic humanitarian consequences, displacing 50,000 to 100,000 individuals in recent weeks," the statement said.
"These actions stand in direct conflict with the government's stated aim of a political solution to the conflict."