The "one child" policy started around 1979-80, after Deng Xiaoping came to power in 1978. Exceptions are allowed for minorities (8% of the population), if the first child is born disabled, for rural couples if the first child is not a boy, and for overseas couples. Parents are fined for children in excess of the policy.
Parents lavish care on their one child. Single children are called "little emperors."
The first single children are about now reaching marriage age. If two single children marry, they are allowed two children.
Young urban Chinese families want to own two things: a car and an apartment. An average apartment costs 15,000 RMB per square meter in Beijing, 20,000 in Shanghai. (1 USD = 7.4 RMB approx.) That's about $225,000 for a 900 square foot apartment in Shanghai.
The current generation is the first generation to use home mortgages to purchase an apartment.