Most facilities are secondhand, donated by charitable foundations or individuals.

"Children can also play badminton in the alley outside," Qi said, "They love playing ping-pong, but we can't afford a table.

"Money has always been our biggest issue as we are not sure whether foundations will continue supporting us next year, and so far we have never received funds from the government for this project," she added.

Sometimes volunteers from universities teach the children handicrafts, environmental protection and personal safety skills in case of fires and earthquakes.

Although demand is huge, Qi estimated that less than 10 NGOs in Beijing provide services like those offered by her organization.

There are no reliable statistics to show how many rural children go to cities during the summer school holiday, which lasts nearly two months.

A report by the All-China Women's Federation in May said there are almost 100 million minors whose parents are migrant workers. Of these, 61 million are "left-behind children", which means they are growing up in villages without their parents.

Safety concerns

"During summer, most migrant workers' children are left at home unsupervised, so safety is a big issue," said Sun Heng, director of the Migrant Workers' Home in Beijing, an NGO dedicated to improving the rights of the migrant population.

"There are a lot of demolition and construction sites in these communities. Imagine their children running around; the chances of them getting hurt are worryingly high."

He said the media often reports on children being drowned or hit by cars, and said they are also vulnerable to child traffickers and sexual predators.

On Aug 8, a 13-year-old girl was left alone in her parents' dorm in Taiyuan, capital of Shanxi province, and was sexually assaulted by a migrant worker who lived in the community, according to the Shanxi Evening News.

China National Radio also reported on July 15 that a court in Ningbo, Zhejiang province, had found migrant workers' children account for 70 percent of all juvenile victims in sexual harassment cases.

Children are not only the victims of crime, but also sometimes become involved in criminal activities themselves, partly due to the lack of parental guidance.

Yang Chang, a judge in Beijing's Mentougou district, said summer is a peak time for crimes committed by minors, especially migrant workers' children, with intentional injury and public disorder the most common offences. Most defendants are aged 12 to 14.

"Young offenders and victims have more time to go out independently and their parents can't watch them at all times," she said, adding that her team gives lectures in schools on child safety.

Sun said the establishment of child activity centers in every community in major cities would also help prevent crimes and accidents.

"What these children lack most is safe places for them to go to play when their parents have to work," said Qi from the Mulan Activity Center.