Hassam (pronounced HASSm;) (known to all as Childe, pronounced like child; named after an uncle) was born in his family home on Olney Street (Meeting House Hill) in Dorchester, Boston, in 1859. His father Frederick was a moderately successful cutlery businessman with a large collection of art and antiques. He descended from a long line of New Englanders. His mother, Rosa, a native of Maine, shared an ancestor with American novelist Nathaniel Hawthorne. His father claimed descent from a seventeenth-century English immigrant whose name, Horsham, had been corrupted over time to Hassam. With his dark complexion and heavily lidded eyes, many took Childe Hassam to be of Middle Eastern descent - speculation which he enjoyed stoking. In the mid-1880s, he took to painting an Islamic-appearing crescent moon (which eventually degenerated into only a slash) next to his signature, and he adopted the nickname "Muley" (from the Arabic "Mawla", Lord or Master), invoking Muley Abul Hassan, a fifteenth-century ruler of Granada in Washington Irvings novel Tales of the Alhambra.
Hassam demonstrated an interest in art early. He had his first lessons in drawing and watercolor while attending The Mather School, but his parents took little notice of his nascent talent.