Dash for Khartoum by G. A. Henty (1832 - 1902)

When a nursemaid mixes up her baby boy and the baby of the family she works for, the family decides to keep both. Years later, the nursemaid returns, intent on using the boys to get money. When the boy she chooses first refuses to help and instead runs away, his adopted family is willing to do everything they can to rescue him. But will it be enough when war threatens in the Sudan--the runaway's destination? - Summary by Adele de Pignerolles