CHILDHOOD LOST

"Single children lack the fun of playing, working and even fighting with siblings, which used to be crucial parts of childhood," Zhang said. "Such experiences help shape children's personality and through conflict and solutions, children learn to compromise and get along with others."

Many single children are spoiled at home and lack group activities, said Prof. Zhou Xiaozheng with Renmin University: "They are more prone to psychological problems than their peers with siblings."

The China Association for Mental Health estimates that 15 percent of children under 14 have psychological problems: at least 20 million children.

Before he went to study in the United States in 2012, Chen Zhengwei, 18, attended six different schools in Guangzhou, Nanning and Beijing. Each time his parents changed jobs, he would have to change school, sometimes even before he got to know his classmates.

"My parents were busy all the time. I had no siblings at home and no friends at school. The solitude was overwhelming," said Chen. "I became addicted to computer games at seven, and only overcame the addiction after I left China at 16."

His parents took him to counseling, but he refused to follow the doctor's advice. "I felt it was not my fault, so I didn't want to make any changes."

Chen resents his parents for his bitter childhood. "They could have given birth to another child, or given me a stable environment with friends."

But for Chen, born in 1996, a sibling was simply out of the question even if his parents had the desire. The couple are urbanites and they both have siblings themselves. Second children in those days were only allowed to rural residents or parents whose first child was disabled. The policy loosened over the years to marriages where both were single children themselves and to wealthy people willing to pay at least 200,000 yuan. Since the end of last year, if only one parent is a single child, couples are allowed a second.

Over the decades, the one child policy has cut China's population by about 400 million, reckons Beijing University professor Guo Zhigang. Average annual births dropped from 20 million in the 1980s to 15 million in 2000, and the proportion of minors in the total population shrank from 33.6 percent in 1982 to 16.6 percent in 2010. About 218 million people in China have no siblings, according to demographer Yi Fuxian, who made the calculations in 2012 based on national census data.

Yi, -- author of "Big Country in an Empty Nest", a book that blamed the one child policy for a shrinking working population and rapidly aging society -- called for an end to birth limits at least a decade before last years' policy change.