As China has developed, many millions of people have moved from the countryside to huge cities to work in factories. But their children have not been taken with them.
BBC's Newsround hears from one child who has been "left behind".
(http://www.bbc.com/news/world-asia-china-35994479?ocid=socialflow_facebook&ns_mchannel=social&ns_campaign=bbcnews&ns_source=facebook)
