Answer:
Children were sold
Step-by-step explanation:
Slave families were rare because most of the families were sold to other owners. In these days the slaves were not considered as persons but were actual property. When an owner saw an opportunity he would breed slaves and sell the children for profit.
While it is indeed true that non of them were given real names this was not the true reason. Later on, it would be harder to reunite for this reason and there have been claims that some of the parents killed these children before they could be sold off.