No idea what /u/SamSlate is implying with that remark and whether it is aimed at me or the work in question. No, I mean that this was happening, that impoverished parents sold or pledged their their children, you can go find such contracts from 2nd mil. BC Babylon or 11th century Italy1. There is nothing outlandish about it. I mean exactly what I am saying here. Now, if one is interested in that particular section of a book, I recommend reading the reference which is given and research further, I am not familiar with that area to comment.
Yes. People sold and pledged their children. This is so ubiquitous and noncontroversial any work on the subject will go through - I wil just link to this bibliography at the end of a post (it does not go into medieval period though).
Also, almost all historical assertions will have a reference and corresponding work in the bibliography, so one can get them easily and read the referenced work it self. But as said, I know economic and legal historians have been quite critical of some assertions - which is unsurprising, given the nature and scope of the book.
1 Codice diplomatico Amalfitano doc. 85. [1090, Amalfi, a mother hands over her daughter in lieu of a debt.]