There are an estimated 61 million children in China living without one or both of their parents. A book of letters, diary entries and pictures by these young people has proved a sensation, and revealed the rich inner-lives of some of the country's most vulnerable people. Sun Yuanqing reports from Anlong, Guizhou province.

Yang Zhengxing is 13. Like many of his peers in the mountainous county of Wanfenghu in Guizhou province in Southwest China, he looks much younger than his age because of malnutrition. His mother left the family when he was 4, and his father works as a construction worker in Zhejiang province, some 25 hours' train ride from home, and returns only once a year. Yang lives with a younger brother and his grandparents who are both in their 70s. Despite his small frame, Yang is considered a major labor source in the family. He toils in the corn field with his grandfather and takes care of his brother. Whatever happens in his life, he records it in his diary.

"It's like having someone to talk to," he says. "Putting it on paper makes me feel better than burying everything in my heart."