Milos Raonic, Roger Federer, Caroline Wozniacki and Novak Djokovic pose with Marvel characters ahead of the Australian Open in Melbourne on Saturday. PIC/Getty Images

Swiss tennis ace Roger Federer had a couple of superheroes for practice during Kids Day ahead of the Australian Open. Milos Raonic, Caroline Wozniacki and Novak Djokovic joined him during the light-hearted event in Melbourne.