As summer mercury zooms up toward the 35-40+ C range, China's ocean parks, island destinations and water-based attractions are in hot demand, with online searches for such commercial leisure activities surging 55 percent in July from June, said Trip.com Group, China's largest online travel agency.

Even sales of park entry tickets and other activities have risen significantly nationwide. In fact, sales of ocean parks' admission tickets doubled in July from June as families traveled with their children, Trip.com found.

"Summer vacation is the peak period for 'parent-child consumption', and theme resorts such as ocean parks boast multiple attributes such as 'parent-child activities', study and research tours, and night tours, which are highly favored by 'parent-child families'," said Wang Yalei, a researcher at Trip.com.

"This summer, such resorts are expected to engage in fierce competition in the design of theme room types, service upgrades, prices and other dimensions to attract more parent-child visitors," Wang said.

For instance, Shanghai Haichang Ocean Park has upgraded park tours and interactive activities. Its night admission session has started operating daily in summer. From early July to late August, the park is organizing a water-splashing festival that will see various cartoon and game characters putting up performances and interacting with tourists.

On July 20, some 41,000 tourists visited the ocean park, up 65 percent year-on-year. The three major theme hotels that are affiliated with the ocean park were fully booked for 10 consecutive days, with over 90 percent of the visitors coming from places other than Shanghai, it said.

This summer, nearly half of tourists traveling domestically have been families traveling with their children, and the booking volumes of related travel products and hotels in July have jumped significantly over June, Trip.com said.

The average level of spending has also exceeded that of last year. A number of major scenic spots have upgraded their services and are offering complimentary admission tickets to attract more family travelers this summer, the online travel agency said.

For instance, a resort affiliated to Shanghai Haichang Ocean Park has designed six kinds of theme rooms for children, including rooms whose decorations depict dolphins, penguins and coral.

Water parks such as Zhuhai Chimelong Ocean Kingdom in Zhuhai, Guangdong province, the water amusement park at Water Cube in Beijing, and Qingdao Polar Ocean World in Qingdao, Shandong province, have emerged as hot spots this summer, according to Tuniu Corp, a Nanjing, Jiangsu province-based online travel agency.

"Ocean parks and water parks combine the features of cooling and fun, making them great places for urban residents to cool off on weekends and relax with their children," said Cai Miao, East China product manager of Tuniu.