Conflict in South Sudan has led to the biggest refugee crisis you don't know about

A million children have now fled South Sudan, and a million more may be displaced within the country in the midst of what one senior U.N. official called the most worrying refugee crisis in the world, the BBC reported on Monday.

As refugees fleeing the ongoing Syrian Civil War streamed into Europe, a separate crisis was raging in the relatively new nation of South Sudan, leading hundreds of thousands of people to flee for their lives. 

Now a total of 2 million children are displaced amid a national conflict that started back in 2013, according to a report released Monday by UNICEF and the UNHCR, the U.N.'s refugee agency.

"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," Leila Pakkala, UNICEF's regional director for Eastern and Southern Africa, said in the report. 

"Add this to the more than 1 million children who are also displaced within South Sudan, and the future of a generation is truly on the brink."

As ABC News reported on Monday, South Sudan seceded from Sudan in 2011 after years of devastating civil war. In 2013, a violent internal conflict broke out in South Sudan between two sides aligned along ethnic lines. 

According to ABC News, both sides have been accused of atrocities that put children at risk, including recruiting children to serve as child soldiers and sexually assaulting and killing civilians. 

According to the new report from the UNHCR, "more than one thousand children have been killed or injured since the conflict first erupted in 2013," suggesting a potentially deadly alternative for the million children who have fled South Sudan for surrounding countries.

Compounding the violence and upheaval is widespread hunger and malnutrition in South Sudan. As ABC News reported, more than 250,000 children in South Sudan are malnourished.

Refugees fleeing South Sudan, the majority of whom are children, have arrived in Uganda, Kenya, Ethiopia and Sudan, according to the report, where they remain in dire need of humanitarian aid including food, shelter and medical care.

The U.N. is calling for $181 million in aid to help these refugees, according to the report. So far, it's only received a little more than half that amount. 

"No refugee crisis today worries me more than South Sudan," Valentin Tapsoba, UNHCR's Africa bureau director, said in Monday's report. 

"That refugee children are becoming the defining face of this emergency is incredibly troubling," Tapsoba said. "We, all in the humanitarian community, need most urgent, committed and sustainable support to be able to save their lives."