These kids are always on the ball

After chasing down dozens of loose balls and accurately rolling them between baselines in the sweltering Beijing heat, 10-year-old Wang Siyuan finished her 30-minute tryout session drenched, but delighted.

An avid tennis fan from the age of 7, Wang knows a thing or two about serving as a ball kid - one of the jobs most coveted by young aficionados of the sport.

"Physically, it's a hard job ... but mentally, it's rewarding and fulfilling," said Wang, who hails from Ergun, Inner Mongolia autonomous region.