A Song for My Mother - that's Aizam's song. It's the one he sings for money outside the manhole in which he lives in Ulaanbaatar, Mongolia's capital city. Without this source of income, he'd be forced to pick pockets or steal whatever he could find, the only means of survival for the other children he lives with.

Aizam's voice is a gift from his father, a famous singer known throughout the country. But Aizam doesn't speak of him. His parents divorced when he was a small child. His mother remarried soon thereafter, but her husband threw the boy out because he didn't want to care for a child that was not his own. Aizam wandered back to his father's house and knocked on the door. No one ever answered. Aizam was eight years old.

Eventually, he joined a group of children who lived in a manhole beside a movie theater. In the seven years since, he has seen his father several times strolling down the street with his new wife. They walk past and ignore him, as if he is not there.

"He has lost me," Aizam says.

There are homeless children in virtually every country on Earth. But the plight of those in Mongolia is particularly desperate. Long, harsh winters drop temperatures well below -30 F (-34 C) in one of the coldest capital cities in the world. Many children go underground, living in manholes under the streets to stay alive. They survive as scavengers, pickpockets and laborers working in the city's black markets.

These photographs were taken for the Christina Noble Children's Foundation.