Sing was born on 2 March 1886 in Clermont, Queensland, Australia, the son of a Chinese father and an English mother. His parents were John Sing (c. 1842–1921), a drover from Shanghai, China, and Mary Ann Sing (née Pugh; c. 1857–unknown), a nurse from Kingswinford, Staffordshire, England. Sing's mother had given birth to a daughter named Mary Ann Elizabeth Pugh on 28 May 1883, less than two months before marrying Sing's father on 4 July 1883. It is unclear whether this child was John Sing's daughter as well. A daughter, Beatrice Sing, was later born into the family on 12 July 1893. The three children grew up together on the farm run by the Sings, and all three performed well academically.