Reigning US Open champion Marin Cilic received a surprise birthday blessing from the young Chinese tennis fans he joined for a hit-out on Sunday in Beijing, before the China Open tournament in the Chinese capital.

On Sunday morning, the Croatian joined the Swing for the Stars tennis training camp and did some basic training with the 12 camp members, who were selected throughout the country to join a three-day "weekend with the stars" activity.

The children also presented him with a big birthday cake for his 26th birthday on Sunday.

"It's always a big pleasure to make the kids happy. It's a pleasure I was invited here to play a little bit with them and give them a memory for many years. I hope they will be motivated and try to play tennis and try to be good," Cilic said.

The members of the camp, aged 7-12, witnessed the draw ceremony for the China Open on Saturday and met some of the world's top tennis players in Beijing. Four of them will go to Australia for an international training camp in November.

Cilic also gave the youngsters some advice about adopting a relaxed attitude to the sport, where enjoyment is just as important as success.

"For the kids, the most important thing for everybody is to try to always give your best. You always have very tough days. But it's important to understand that tennis is also a game that you have to enjoy. If the pressure to win becomes too big, it's not good," he said.

"The best result I had was when I was enjoying my game and when I had the most fun on court and still played really well. I think that's the most important thing for everybody."

Cilic, the two-time China Open finalist, will meet China's wildcard player Bai Yan for the first round at this year's China Open, which kicked-off on Saturday.