Roger Federer of Switzerland laughs during an exhibition match on Kids Tennis Day, held at Melbourne Park in Melbourne, Australia, Jan. 13, 2018.(Photo: Xinhua)
Pupils demonstrate smiley cards to greet the upcoming World Smile Day at a primary school in Handan, north China's Hebei Province, May 7, 2019.(Photo: Xinhua)
A smiling child eats pear at a pear planting base at Xiaogang Village in Fengyang County, east China's Anhui Province, on Sept. 15, 2018.(Photo: Xinhua)
Children laugh at a Syrian refugee camp in Bar Elias, Bekaa Valley, eastern Lebanon, on June 19, 2018, ahead of World Refugee Day.(Photo: Xinhua)