Children play on a slide in Taoranting Park in Beijing on Jan. 23. A rapidly aging population and a shrinking workforce are expected to strain China’s economy in the future. (Wu Hong/European Pressphoto Agency)

When China announced it was relaxing its one-child policy in late 2013, marketing director Kang Lu chatted with her husband about whether they wanted a second baby.

“But given our current circumstances, we quickly abandoned the idea,” she said. “It wasn’t a tough decision.”

They weren’t alone. So far, a number of Chinese families have been less than enthusiastic about the partial relaxation of the policy, choosing to stick with one child, often for practical and economic reasons, but also because decades of government propaganda have convinced them that one child really is best.

Experts say this only underlines a looming demographic crisis in China: low fertility rates, a rapidly aging population and a shrinking labor force will inevitably put immense strains on the economy in the decades ahead, and on the government’s ability to pay people’s pensions. It is so severe a problem, some experts predict it could threaten the legitimacy of Communist Party rule.

Yet for many urban couples in modern China, having a second child is no longer an attractive option.

Children dressed in uniform wait to enter their classroom at the Beichuan Red army elementary school in Beichuan, China, on Jan. 21. (Fred Dufour/AFP/Getty Images)

There are no preschools here for children under 3, while the market for nannies is unregulated and tales of neglect are rife. Kang’s parents had moved to Beijing for three years to help look after her daughter, but they now felt too old to help.

Kang also has ambitions for advancing her career but was faced with the prospect of giving up those ambitions — or giving up her job entirely — to care for a second child. In Beijing’s soaring housing market, Kang and her husband couldn’t afford a larger apartment, which they figured they would need if they had a boy. And they were worried that the capital’s smoggy air could affect a new baby’s health.

“The joy and happiness my daughter brought us is worth anything,” she said. “I am 36, and I know this could be my last chance to have another baby. But I very much doubt the joy of having another baby would outweigh these practical obstacles.

“Besides, I am an only child,” she said. “In my mind, one child is good enough.”

China’s controversial one-child policy was introduced in 1980 but partially relaxed just over a year ago amid mounting fears of an aging population and shrinking labor force.

Under the new rules, couples in China are allowed a second child if either parent was an only child. Rural couples can have a second if their first child is a girl.

The new policy was rolled out across the country last year, with Beijing one of the first provinces to relax the rules. Still, only 6.7 percent of eligible couples in the capital applied for permission to have a second child in the 10 months since the rules changed; nationally, interest was higher, but with fewer than 1 million couples applying, it was still below government forecasts.

The data reflect how a combination of the one-child policy, rapid urbanization and rising incomes have dramatically reduced fertility rates in China. That may have stabilized the country’s population, but it has brought in its wake a new set of problems.

As its population ages, China is racing toward a “demographic precipice,” said Wang Feng, a professor of sociology at the University of California at Irvine, predicting a crisis so deep that it could challenge the legitimacy of the Communist Party.

The nation’s fertility rate, of 1.4 children per woman, is way below that of the United States and the developed world average, and will lead to a rapid aging of society. That means a substantial decline in the supply of young labor to power the economy and a rapidly escalating number of old people.

As the economy slows, government revenue growth will slow, even as the financial burden from the elderly rises. Sooner or later, Wang says, that means the government will run out of money to pay for pensions or finance growing health-care costs.

“This challenges the legitimacy of the political system, which claims to be able to do this kind of thing,” he said. “And I am not talking about the long and distant future — I am really talking about the next 10 or 15 years.”

China’s working population fell for a third straight year in 2014, declining by 3.7 million, to 916 million people, according to data released last week , in a trend that is expected to accelerate in years ahead. Meanwhile, the number of people aged 60 and above will approach 400 million, or a quarter of the population, in the early 2030s, according to United Nations forecasts, from one-seventh now.

In December, a group of more than 50 leading demographers came together in Shanghai to appeal for further relaxation in family-planning policy, although experts say that even a total abandonment of the one-child policy tomorrow would do nothing to relieve the problem for decades.

Yet the government is dragging its feet, unable to completely turn its back on a policy that has empowered (and often enriched) thousands of often corrupt officials for decades.

Mao Qu’nan, the chief spokesman for the government’s National Health and Family Planning Commission, says that the size of China’s population is still a more pressing problem than the fact that it is aging.

Those who say otherwise, he said, “have malicious intentions to damage the Chinese government in the name of birth control.” Family-planning policy would be relaxed further over time, but the government had no timetable in mind.

Wang said the spokesman is “deeply trapped in the outdated belief in birth control.” He said that “incompetent, irresponsible and unaccountable officials” refuse to change a policy that has caused untold misery and will soon have serious economic and political consequences.

Birthrates in East Asia are generally low, demographers note, and an aging population has emerged as a problem in Japan. In China, families’ driving ambitions for their offspring to succeed means many parents are happier to concentrate on a single child.

“My husband and I provide everything we can for our daughter,” Kang said. “We pay for her to go to her favorite ballet class. We plan to send her overseas when she grows up. But if we had another baby, I don’t think we could do all this for both of them.”

In contrast, freelance writer Li Yue had a second baby by accident. Conceived before the policy was relaxed, she was lucky that the baby was born after the rules changed and she escaped a heavy fine. But she did not escape society’s disapproval.

“Many people have been brainwashed by one-child policy propaganda, including my mom,” she said. “When I told her I was having a second child, she thought it was unacceptable. She didn’t call me or talk to me for a month.”

Li said she was an only child, as were all of her six cousins, and they all used to believe one child was best.

“Before my first daughter came into the world, I only planned to have one baby. But when I saw my daughter, the joy, the happiness made me want to have more babies,” she said. “Now, my mom loves my younger daughter very much. She has moved to our place to help look after her. And she has even started to persuade other people to have a second child.”

Xu Jing contributed to this report.