Korean children have been found to be about 3 to 4 centimeters shorter than their South Korean counterparts, according to a 2009 study published in the journal Economics and Human Biology.
Nearly 28% of North Korean children suffer from stunting, according to the U.N. Office for the Coordination of Humanitarian Affairs.
Fifteen years after meeting the first of these street orphans, Jung is still helping defectors escape, working from a small, cluttered basement office in the South Korean capital.
'Hugs and comforts'
For a decade in North Korea, Yoon Hee roamed the streets, slept in crevices and picked rice off the ground that people had dropped.
"I appreciated every single grain of rice," she said.
Every night, she had the same concern: "Where am I going to sleep tonight? How can I survive?"
In Ryanggang province where she lived, the average monthly temperature can fall below freezing during the winter months, according to the World Food Programme.
Yoon Hee learned survival skills fitting of "The Hunger Games" -- where to scavenge for food, where to sleep, how to stay warm, how to keep safe. She curled into a fetal position in a nook under the windows of houses.
"Sometimes, I wrapped my feet with a plastic bag because it was too cold."
She slept alone, except for her thoughts of her mother.
"When I almost was starved or freezing to death, the only things I wanted from her were hugs and comforts. I thought that was happiness."
But she couldn't recall a single hug from her mother.
Surviving in a new home
Hyuk lost his mother when he was 6, then his father when he was 11.
After his father died, he lived with a group of six other orphan boys in North Hamgyong province, located at the northern most tip of the country.
"We started a fire together, but we still couldn't sleep because it was so cold," he said. "We just warmed ourselves with the fire at night and we mainly slept during the day when the sun was shining.
"During the night, we needed to find food to eat. We sometimes stole food from others and gathered food from here and there."
When something went missing in the neighborhood, the blame automatically fell on Hyuk and his friends, even when they had not been involved. The children would be taken to the police station and tied to chairs, he said.
"The police would then automatically accuse us of stealing because they assume we would have stolen since we don't have parents. They hit us, tie us up, and torture us. There was no one to defend us."
Hyuk, now 21, attends Hangyeore Middle-High School, where he sleeps in a bed inside a heated dormitory. The school serves three warm, buffet-style meals a day, and students can pile as much food as they'd like on their metal trays.
In the school's hallways, girls with sleek black hair and boys with long sweeping bangs are busy texting and taking pictures of themselves on their phablets -- a combination smartphone and tablet. Their crisply ironed school uniforms would not be out of place at an English or American boarding school.
It's a vastly different scene than the childhood Hyuk describes. The blur of hunger, cold and countless police beatings has been replaced by soccer and basketball.
The school, set up by the South Korean government, does not charge tuition.
The North Korean orphans who escape to South Korea often struggle to catch up in a competitive environment where their counterparts have had years of schooling and private tutoring.