We have quite a few pre-industrial texts that contain routine mentions of child labor. For one of the best known:

The child grew up. One day, he went out to his father among the reapers. [Suddenly] he cried to his father, “Oh, my head, my head!” He said to a servant, “Carry him to his mother.” He picked him up and brought him to his mother. And the child sat on her lap until noon; and he died.

Then Samuel asked Jesse, “Are these all the boys you have?” He replied, “There is still the youngest; he is tending the flock.” And Samuel said to Jesse, “Send someone to bring him, for we will not sit down to eat until he gets here.”

But Saul said to David, “You cannot go to that Philistine and fight him; you are only a boy, and he has been a warrior from his youth!” David replied to Saul, “Your servant has been tending his father’s sheep, and if a lion or a bear came and carried off an animal from the flock, I would go after it and fight it and rescue it from its mouth. And if it attacked me, I would seize it by the beard and strike it down and kill it. Your servant has killed both lion and bear; and that uncircumcised Philistine shall end up like one of them, for he has defied the ranks of the living God.

This was actually David admitting that he goes the extra mile, as hired shepherds were not required to fight off predators, but here we have a child (probably an early adolescent) casually noting that he had a job where he killed a bear. This would not have been included if children his age never worked as shepherds in pre-industrial society.