The youngest documented mother was 5 years old, in the 1950's. She was in some backwards village in Peru? Chile? One of those S.A. countries. Her stomach was swelling and they though she was possessed by evil spirits. They took her to the village shaman. To his credit, the shaman suspected a tumor and sent her to a hospital several hundred miles away. When they realized what was up, they arrested the girl's father, later releasing him for lack of evidence.
The girl is still alive, married and has several other children now (none before she was about age 19). The child, who was raised by his grandparents died about 20 years ago.