If they are taking children from the streets, there would not be any ransoms. That does not mean they are not being sold.

[And if 9S truly wants a crash course in all the terrible things humans are capable of, Lan Wangji will set aside plenty of time to have that discussion with him--but, perhaps, not in the presence of the children they're trying to rescue. Bennett may not be old enough to quite grasp the content of their conversation, but Bianca certainly is, and even though Lan Wangji is speaking quietly, he's not exactly whispering.]

For now, we must focus on making sure these two are not targeted again.