Not quite
that young. Hunter gatherers usually have their first pregnancy at fourteen, not twelve/thirteen. It was loosely the same in agricultural societies
almost everywhere, with the German tribes of antiquity being a notable exception (add two years) that through the migration era eventually became the European norm, with the age of first childbirth slowly increasing over time, a process which in turn carried off to the Americas.
In the 19th century, the average woman in the US had her first child at age
23. Something that seems to have been loosely the same across the catholic/protestant world, judging by
Finland.
To say that having sex with a twelve/thirteen year old girl and her giving birth at thirteen was outside the norm of 19th century North America would be an understatement. Yeah, prostitutes that age was a thing, but that was
also outside the social norms and at any rate, can safely be considered coerced. For any social class higher than literal prostitutes and pimps, it was unthinkable. When it happened, it was a social catastrophe.
Slavery on the other hand, made it possible without meaningful repercussions.