People did this all of the time, not sure about the Greeks specifically (but I would assume they did also).

If you were dead broke, you married off one of your kids… if you couldn’t do that, you sold them.

People still do this TODAY.

Imagine if you couldn’t feed your own children. Wouldn’t selling them be preferable to watching them waste away until their inevitable demise?

(not that Jefferson did it because he was starving, he just needed some walkin’ around money)