Liu Zhe, 33, a cashier at a supermarket in Shanghai, said, “Our lives were dictated by an arbitrary policy in circumstances that were entirely out of our control. Sometimes I wonder whether it is fair.”

Those entering adulthood now will form the backbone of Chinese society at a pivotal moment, as the ranks of the elderly grow rapidly and as the economy faces new strains, including a shortage of workers.

In interviews, members of the one-child generation said they grew up hearing that they were among the most blessed generations in Chinese history, having avoided the poverty and brutal conflicts experienced by their parents and grandparents, only to realize later that they would have to shoulder the burden of taking care of aging parents, in-laws and children without the support of siblings.

“We were told we were spoiled little emperors,” said Zhang Cheng, 22, a university student in Beijing. “But they didn’t tell us we would be the only generation that would have to face these obligations alone.”

After the change to the one-child policy was announced late last month, only children revived a familiar thought experiment: What would life be like with a brother or sister?

Li Luochen, 26, who works in marketing for a video game company, said that as a child she enjoyed receiving undivided attention from her parents. But now that she is an adult and her parents are urging her to have children, she wishes she had a brother to turn to.