Drat, that last theory won't wash either.
William Macleod and Julianna Mary Esner were married in Reading, Berkshire in 1848 and had two children, William, born 1850 and Charlotte Mary, born 1852, both in London Marylebone. The 1851 census lists them in London: William Macleod, 40, fruiterer and greengrocer; wife Julianna, 26, and son William F, 5 months, all born London.
Maybe it was a case of a drunken father rather than a drunken stepfather.