Grossmith had a younger sister, Emily, and younger brother, Weedon. In 1855, he went to boarding school at Massingham House on Haverstock Hill in the district of Hampstead. There he studied the piano and began to amuse his friends and teachers with shadow pantomimes, and later by playing the piano by ear. His family moved to Haverstock Hill when young Grossmith was 10, and he became a day student. At the age of 12, he transferred to the North London Collegiate School in Camden Town. He was back in St. Pancras by age 13. He was an avid amateur photographer and painter as a teenager, but it was his brother Weedon who went to art school. The Grossmith family had many friends engaged in the arts, including J. L. Toole, Ellen Terry, Henry Irving, H. J. Byron, Tom Hood, T. W. Robertson, and John Hollingshead (later, the manager of the Gaiety Theatre, London).