Indoor playgrounds are proving an oasis for parents looking to allow their children to stay active safely as Japan sweats through a summer of record-breaking heat.

Parents are turning to playgrounds in air-conditioned shopping centers and other commercial enterprises when they would typically use public spaces outdoors.

"I fear the danger of heatstroke in the park," said a young mother who brought her 2-year-old boy to the Kid-O-Kid indoor playground in Yokohama on a weekday afternoon in late July.

The indoor playground, which is about 190 square meters, has crash mats, slides and other child-focused equipment so youngsters can run around safely in an area dedicated to them.

The mother, who is nine months pregnant with her second child, bought a 12,800 yen amusement passport (about $116) which gives her and her son unlimited access to the playground during the summer holiday period. She brings him there several times a week.

"At home, I would be showing him DVDs, but here he never gets bored," she said.

The playground is one of 21 operated in 11 prefectures by Bornelund Inc., a Tokyo-based toy company. The number of visitors recently increased sharply, especially in parts of western Japan which have suffered the worst of the summer heat.

Peak hours are between 2 p.m. and 3 p.m. when the heat outside is most brutal. Many parents say they use the indoor playgrounds because it is difficult to keep their children occupied at home, a Bornelund official said.

The number of visitors to Pure Heart Kids Land, an indoor playground in Kakogawa, Hyogo Prefecture, increased 40 percent on July 15, compared with other Sundays.

According to rough estimates by the Fire and Disaster Management Agency, ambulances were dispatched to carry a total of 22,647 people to hospitals for heatstroke across Japan during the week from July 16, and 65 of those died. Both figures are the highest on record.

Exposure to the sun and heat has even made outdoor swimming pools no-go zones, forcing elementary and junior high schools to close many across the country.

These days, parents are particularly sensitive about health warnings, said an official at Fantasy Kids Resort, a Tokyo-based company operating indoor playgrounds in six prefectures.

"We saw an increase in visitors when PM 2.5 air particle pollution became a topic in the news," a company official said. "It seems like parents who are worried about heatstroke this year are visiting our playgrounds and avoiding parks and swimming pools."

Even so, Tatsuhiro Yamanaka, a pediatrician who heads Safe Kids Japan, a nonprofit organization that educates people about how to prevent childhood injuries, warns that kids' temperatures can rise even in air-conditioned facilities due to physical activity.

"Parents shouldn't just let their kids play with no rest. They need to keep them hydrated and check their temperatures every 30 minutes," Yamanaka said.