China's only children are often spoiled "little emperors"
Officials in Shanghai are urging parents to have a second child, the first time in decades the government has pushed for more babies.
A public information campaign has been launched to highlight exemptions to the country's one-child policy.
Couples who were both only children, which includes most of the city's newly-weds, are allowed a second child.
The move comes as China's most populous city becomes richer and older, with the number of retired residents soaring.
"Shanghai's over-60 population already exceeds three million, or 21.6% of registered residents," said Zhang Meixin, a spokesman for the city's Municipal Population and Family Planning Commission.
He said the current average number of children born to a woman over her lifetime was less than one.
Micky Bristow, BBC News
Chinese and foreign experts have been saying for some time that China needs to change its strict family planning rules.
If the country continues as it is, the proportion of elderly people in society will continue to increase.
This is a problem because it will leave a smaller group of workers paying for the country's retired population.
But central government officials have consistently ruled out changing the national family planning policy.
They still believe that China has too many people - an opinion shared by almost everyone in the country.
That has left individual cities, such as Shanghai, to think up ways of coping with their own ageing communities.
"If all couples have children according to the policy, it would definitely help relieve pressure in the long term," he added.
Decades of a strictly enforced one-child policy has produced new strains across the population and prompted exceptions in some family categories. Rural parents are also allowed to have a second child, if the first-born is a girl.
In Shanghai, family planning officials and volunteers will make home visits and slip leaflets under doors to encourage couples to have a second child if both grew up as only children.
Emotional and financial counselling will also be provided, officials said.
By 2020, the country's most populous city is expected to have more than a third of residents aged 60 or above.
According to the US-based Center for Strategic and International Studies, by 2050 the country will have just 1.6 working-age adults to support each retired person, compared to 7.7 in 1975.
The state-controlled newspaper China Daily quoted one salesman who said he was cheered by the new attitude.
"I'm not sure, but such policy really gives us one more option. If family finance permits, I want to have two kids with my wife in the future," said 25-year-old Xiao Wang, who works at a local company.
Others were less enthusiastic.
"I don't think we will have a second kid," said 26-year-old Xiao Chen, an office worker. "After all, it is stressful work raising a child."
Couples who ignore China's birth control policies usually pay fines and may face discrimination at work.
The many only children of China have earned the nickname of "little emperors" for the love and treats lavished upon them.
China's birth-control policies have been hugely controversial at home and abroad, as enforcement has involved forced abortions and other abuses.
It has also been blamed for a gender imbalance, as a traditional preference for boys has persuaded some parents to abort girl foetuses.