((When someone is made a slave, they become, for all practical and lawful purpose, an animal. And animals have no rights, they own nothing, rather it is them which is owned. In this respect, trading them is no different to selling a cow, or a pig.
Regarding children, female orcs especially, show some care for children of other races, slaves however are animals, so the care shown would be purely out of self interest. A cow with 4 legs is of more use than a cow with 3.
Orcs love proving they ate superior to other races, enslaving them is just another way in which we would prove our dominance, infact it would be seen as bub'hosh to take many slaves, it shows your strength.))