Curtis was born in Yarrawonga, Victoria, Australia, the daughter of Carmencita Ojales, a Filipina from Bolinao, Pangasinan and James Ernest Curtis-Smith, an Australian lawyer. Her father is a World War II veteran and married Carmencita Ojales in 1982. Her younger sister, Jasmine, is also an actress. On their father's side, they had a half-sister named Clare who died in 2007 due to a cardiovascular disease at four months old. Curtis, being half-Filipino, would visit her mother's relatives in the Philippines with her family. In 1997, 12-year-old Curtis was approached by a talent scout to ask if she would like to get into a children's beauty pageant. Her father feared that it was a scam, while her mother wanted her to try it. Without her father's knowledge, Curtis then started to go to different talent agencies, and met her first boyfriend Anthony. By that time, she and her family decided to stay permanently in the Philippines. Curtis could not speak or understand the Filipino language at the time, and so had to take classes.