Nobles can't be seen as inherently better than slaves if slaves have time and resources to attain the same education as them. This takes away the time and does something useful for the superior people.

It's well studied how introducing women to the labor force increased work demand and decreased pay (Not saying it was bad, just stating the obvious consequences). You can get another easy boost by also properly utilizing the kids as a human resource. Now the whole family needs to work to stay over the poverty line. Perfect.