My 4x great grandmother was 12 when she was married to her step-brother and 13 when she had her first and only child. I found a book that states;
"Malinda Yoder, was a wife and mother in her thirteenth year, was married to John Bixler, her marriage taking place at the age of twelve years, which is an occurrence never before known in the United States."
I don't know how accurate the book about her being the youngest ever to be married but I do have a census, a Mennonite vital record, probate record, gravestone, and her obituary which all confirm her young age.
She then died at the age of 13 of typhoid fever.