Li Xinru (second right) with her fellow students at the primary school in Yangfan village, Shanxi province. Zhang Yuchen / China Daily

Ignorance, humiliation

Some cases never come to light because the families fear the public humiliation that can accompany revelations, but other factors are also in play, including ignorance.

"The (sex) education children receive is usually inadequate. Some of the kids don't even understand what has happened to them," said Zhou Liping, director of the children's health department at Shanxi Children's and Women's Hospital.

There are no reliable statistics about the sexual abuse of children because the figures only relate to cases that are reported and go to trial. "Many children have been sexually assaulted, but we have no idea of the exact number," admitted Han.

Even the figures that are available may not tell the true story because the method of case classification makes assessment almost impossible.

"One reason is that the cases are divided into different categories, such as 'school-based sexual abuse' or 'rural sexual harassment'. The personal circumstances of the children are not stated explicitly, so it's hard to know whether they are members of the 'left-behind' group or not," said Han.

Lonely, frustrated

Of course, sexual abuse isn't the only problem facing left-behind children. Loneliness, frustration and feelings of being unwanted can also cast a shadow over these young lives.

Li Xinru stood alongside her smiling fellow students, frowning silently. The 6-year-old is one of three left-behind children who attend a village school in Linfen, Shanxi. While the other students played happily, Li rarely looked happy.

Her mother works at a printing factory in Beijing and her father is a laborer in Inner Mongolia, so the first-grade student has been left with her grandparents. Her two older brothers attend a middle school in a nearby village.

Her approach to strangers is markedly different from that of her peers. She is likely to respond to a gift, such as a snack, without a word of thanks or even the slightest change of expression.

She seldom responds to questions and is withdrawn. Her answers usually consist of just a few words: To the question "When do you call your mom?" her answer was "Dark", meaning after nightfall.

When the school held an event to mark a large donation to its building fund, the other left-behind students were surrounded by family members. Li, however, arrived alone. When asked where her grandparents were, she replied, "Watching TV at home". Her expression grew graver and sadder the more she was questioned.

Although she finds it hard to open up to strangers, she reacted quickly when asked, "Who do you prefer to be with, grandpa or your grandma?"

"I like mom most," she said. She made no mention of her brothers.

Company rules mean Li's mother can't take phone calls until after 8 pm and she only sees her children once a year, at Spring Festival. The only dream Li can express freely is, "To go to Beijing and be with mom."

Outside the gate of Li's primary school in Yangfan village, a group of locals leaned on a wall next to a grocery store and kept a watchful eye out for strangers.