They must "retire" at age 16.

"Some are already in college and come to help during the China Open," Han says.

Some work as trainers at the camps.

She says their experiences at the international opens have helped some to stand out when applying to study overseas.

Wei Daipeng worked in the Australia Open for the first time this year.

The 14-year-old was chosen with five other candidates from the China Open, where he has served for six years.

"Every day in Australia was unforgettable. I learned a lot and made many new friends," Wei recalls.

"I want to continue until I have to 'retire'. And I want to have a job related to tennis when I grow up."

Wei and others came to volunteer at the training camp once they heard about it.

"It's also a good chance to reunite with my friends. So, we come."