When Joseph Song was a young boy, he was one of many Chinese children who roamed the streets working for the little money he would never see.

These days, the 19-year-old helps run a sanctuary for street children at what used to be an old chili factory.

More and more Chinese children from impoverished families are sold in what amounts to a slave market. Poor families sell their children to "ren fanzi", which means "a dealer of children".

They are told their children will work in a factory. Instead they are forced to beg for money or steal on the lonely, violent streets of China where handlers often fight over their turf.

All of the money they make goes to their handlers.

Song told CTV's Steve Chao that he was taught to break into cars and steal things as a street child.

"If I didn't come back with enough money, I would be beaten, until I was bloody," he said.

Stacey Hayes runs the sanctuary Song works at. She went to Beijing a few years ago to study Chinese and never left.

She decided to stay after seeing the many children wandering the streets.

The school offers children three meals a day and even classes.

But there is only so much room in the school and the numbers of street children are ever rising.

According to Save the Children UK, there were an estimated 150,000 children living and working on the street in China at last count.

But they say this number may exceed 300,000 if they include the children who work the streets during the day and go home to their families at night.

Most make their living by recycling refuse, begging, performing on the streets and selling flowers.

Save the Children UK estimates that of all the children they have worked with, 70% are boys, 83% of the total are from rural areas and 17% are from urban areas.

Most of the children are aged between 10 and 15 and are either illiterate or have only primary school level education.

Doctors Without Borders is one of the organizations that works with marginalized children in China who escaped or were rejected by their families.

They provide temporary accommodation, medical and psychological care, food and schooling.

"These children have often been exposed to physical and psychological trauma, neglect, abuse, hunger and social rejection," says the Doctors Without Borders website.

With files from CTV's Steve Chao