Andy Wong/The Associated Press

At about 3 p.m. on Sunday, May 6, in Tangxi village in the Chinese province of Jiangxi, a small boy rushed home to his grandparents with fearful news: his siblings and cousins had disappeared under the waters of a pond.

The drowning deaths of five children from the Wang family — Yubo, 6, Yizu and Xinman, both 10, and Baoting and Baolan, both 11, reported here (in Chinese) by The Shandong Business Daily — have thrown a painful spotlight on the hidden price paid by millions of Chinese children for their country’s economic miracle, as China today celebrates International Children’s Day in traditionally big style, with a school holiday for most children.

Nearly 58 million children, almost all in the countryside, are growing up without one – or, often, both – parents, according to state-run media, citing a 2010 survey by the All-China Women’s Federation. Nearly 80 percent are cared for by grandparents, while some are simply left to fend for themselves — 4.2 million, the survey found. Their parents’ absence exposes them to risks that other children may not experience.

Their parents are working in big cities, where they can make far more money, fueling the boom that turned China into the world’s second-biggest economy within three decades. There are more than 200 million adult migrant workers in China, according to official figures. The parents among them may return home once a year to see their “left-behind children,” or liushou ertong, as they are called.

In story after story in the Chinese media, like this powerful one by Xinhua, the state-run news agency, children tell of their sadness at growing up without a mother or father.

The Shandong Business Daily story also drew attention to the difficulties faced by grandparents struggling to raise young children, a challenge even for adults in their prime. The grandparents of the children who drowned, Li Xixiu, 71, and Wang Jiushou, 72, were grief-stricken. Ms. Li hadn’t left her bed for days, the newspaper said.

A commentary in the state-run Guangming Daily asked: “In whose hands are we leaving ‘left behind’ children?” It added: “The pain of this kind of tragedy doesn’t just belong to Wang Jiushou and his family, but is all society’s pain.”

Under the strict residency, or hukou, policies that tie a person to his or her place of birth, social goods such as education, health care and housing are very hard to secure in cities for China’s rural residents, a key reason that so many leave their children behind.

Chinese culture has long relied on the extended family to raise children. But as the country modernizes, people are questioning that.

Children raised by grandparents who might be illiterate, old-fashioned or simply too old to properly care for them may experience emotional and educational problems, according to anecdotal evidence, surveys and media reports. Puberty is a particularly challenging time. Child delinquency is on the rise, according to this story.

In the case of the Wang family, the children were the offspring of two sons and their wives. The four parents calculated the economics of staying home versus going to a city and decided that all four simply had to go, The Shandong Business Daily reported.

Wang Guangzhong and his wife worked on a construction site in the nearby city of Yichun, earning 100 renminbi, or about $16, a day.

Wang Guangjun traveled to Shenzhen with his wife, where they saved 30,000 renminbi a year.

I once assumed that children being raised by grandparents was universally accepted in China. But that assumption was challenged some years ago, when I fell into discussion with a middle-aged taxi driver in Beijing. We compared experiences of being a working parent, and agreed it was tough.

“My parents raised my son,” he said.

“That’s good,” I answered.

“No,” he corrected me. “It’s bad. I hardly know him. And my parents aren’t educated. He listens to my father now, not to me.” His regret was palpable.

A documentary on this subject, “Children Left Behind,” by Catherine Lee Yuk San, a TV producer with the Hong Kong broadcaster TVB Jade, won the 2007 Asia-Pacific Child Rights Award. Receiving the award, Ms. Lee said: “They have parents, but they just live on their own. They live very lonely lives. They eat alone, they play alone. Although it is their basic right to have their parent’s love, concern and care, in reality you can see that they live like an orphan.”

CCTV, the state television broadcaster, interviewed children in Tangxi, the village where the Wang children lived, about their feelings for their absent parents, according to a transcript (in Chinese) published here.

“When do you think of your parents?” an interviewer asked one young child, who was not identified.

“Morning, noon and night,” was the answer.