Washington Post says:
Since introducing the policy more than 30 years ago, China says it has prevented 400 million births. The country asserted in 2011 that it had delayed by five years the future date when the world population will reach seven billion. But one unintended consequence of the policy is a growing number of parents who are suddenly left childless when their only child dies, with no hope of having more. Here is an overview of the one-child policy, the exceptions to the rules and penalties on multi-child families.