Children of migrant workers may suffer serious psychological and emotional damage because of long periods of separation from their parents. There are more than 100 million migrant workers scouring the country for jobs, and in many cases they leave their children behind in the care of friends or relatives. Known as 'left-behind children', they are another side-effect of the mainland's economic growth. Xiao Ying is one of these children. The 13-year-old girl from Fushun county, Sichuan , gave birth to a baby boy in March after she was put in the care of her grandparents, when her parents migrated to find work in the city. 'My wife and I went to work in Chengdu , the provincial capital, four years ago and we only see our daughter and her brother at Spring Festival,' Xiao Ying's father told Sichuan-Online. Xiao Ying said she became pregnant after being raped by her uncle - a crime that went unnoticed by her grandparents, who did not even know she was pregnant until the day she gave birth. Child welfare experts say the case exemplifies the social cost of children being separated from their parents. 'Although there are no figures to illustrate how big a problem this is, I still think there is cause for concern,' said Song Wenzhen , of the State Council's Women and Children Working Committee. 'A long period of separation is not good for building a bond between parents and children,' she said. 'It is also harmful to a child's intellectual and psychological development. 'Grandparents cannot bear the same responsibilities due to bad health and such,' so it is much easier for children left behind by their parents to go off the beaten track, she said. Li Quanmian , of Renmin University's population institute, said: 'A high proportion of left-behind children play truant, discontinue their studies or spend too much time playing computer games. 'The level of education received by children left behind is very worrying,' said Mr Li. 'Their grandparents are usually poorly educated, conservative, and tend to spoil their grandchildren.' Ms Song said 'migrant parents are forced to choose to live apart from their children. Most of them don't like it, but they all realise that there is not a lot that can be done about it'.