The boy's chronic cough and stuffy nose began last year at the age of 3. His symptoms worsened this winter, when smog across northern China surged to record levels. Now he needs his sinuses cleared every night with saltwater piped through a machine's tubes.
The boy's mother, Zhang Zixuan, said she almost never lets him go outside, and when she does she usually makes him wear a face mask. The difference between Britain, where she once studied, and China is "heaven and hell," she said.
Levels of deadly pollutants up to 40 times the recommended exposure limit in Beijing and other cities have struck fear into parents and led them to take steps that are radically altering the nature of urban life for their children.
Parents are confining sons and daughters to their homes, even if it means keeping them away from friends. Schools are canceling outdoor activities and field trips. Parents with means are choosing schools based on air-filtration systems, and some international schools have built gigantic, futuristic-looking domes over sports fields to ensure healthy breathing.
"I hope in the future we'll move to a foreign country," Ms. Zhang, a lawyer, said as her ailing son, Wu Xiaotian, played on a mat in their apartment, near a new air purifier. "Otherwise we'll choke to death."
She is not alone in looking to leave. Some middle- and upper-class Chinese parents and expatriates have already begun leaving China, a trend that executives say could result in a huge loss of talent and experience. Foreign parents are also turning down prestigious jobs or negotiating for hardship pay from their employers, citing the pollution.
There are no statistics for the flight, and many people are still eager to come work in Beijing, but talk of leaving is gaining urgency around the capital and on Chinese microblogs and parenting forums. Chinese are also discussing holidays to what they call the "clean-air destinations" of Tibet, Hainan and Fujian.
"I've been here for six years and I've never seen anxiety levels the way they are now," said Dr. Richard Saint Cyr, a new father and a family health doctor at Beijing United Family Hospital, whose patients are half Chinese and half foreigners. "Even for me, I've never been as anxious as I am now. It has been extraordinarily bad."
He added: "Many mothers, especially, have been second-guessing their living in Beijing. I think many mothers are fed up with keeping their children inside."
Few developments have eroded trust in the Communist Party as quickly as the realization that the leaders have failed to rein in threats to children's health and safety. There was national outrage in 2008 after more than 5,000 children were killed when their schools collapsed in an earthquake, and hundreds of thousands were sickened and six infants died in a tainted-formula scandal. Officials tried to suppress angry parents, sometimes by force or with payoffs.
But the fury over air pollution is much more widespread and is just beginning to gain momentum.
"I don't trust the pollution measurements of the Beijing government," said Ms. Zhang's father, Zhang Xiaochun, a retired newspaper administrator.
Scientific studies justify fears of long-term damage to children and fetuses. A study published by The New England Journal of Medicine showed that children exposed to high levels of air pollution can suffer permanent lung damage. The research was done in the 1990s in Los Angeles, where levels of pollution were much lower than those in Chinese cities today.
A study by California researchers published last month suggested a link between autism in children and the exposure of pregnant women to traffic-related air pollution. Columbia University researchers, in a study done in New York, found that prenatal exposure to air pollutants could result in children with anxiety, depression and attention-span problems. Some of the same researchers found in an earlier study that children in Chongqing, China, who had prenatal exposure to high levels of air pollutants from a coal-fired plant were born with smaller head circumferences, showed slower growth and performed less well on cognitive development tests at age 2. The shutdown of the plant resulted in children born with fewer difficulties.
Analyses show little relief ahead if China does not change growth policies and strengthen environmental regulation. A Deutsche Bank report released in February said the current trends of coal use and automobile emissions meant air pollution was expected to worsen by an additional 70 percent by 2025.