Further, some stories have reported that Facebook says they acquired such parental permission for the minor participants.

Additionally, the minimum age for non-agricultural workers is 14 anyway, so even then they're in the wrong and can't legally hire 13-year olds as contractors or employees. There's also several other rules in the FLSA pertaining to workers under 18 including minimum wage. I have a sneaky suspicion $20 per whatever period it is (unless said period is a few hours) is going to be under that wage.

Not to mention there's a whole lot more can of worms being opened specifically around minimum wage and recording hours that I highly doubt either Facebook or Google were actively managing.

I've never seen that relationship result in anyone being called a contractor and I've signed too many film contracts. I don't know where OP is getting this notion.

Here you can see a VentureBeat reporter – and one who is actually a member of the California State Bar of Attorneys – raise some of the same questions as I have:

https://venturebeat.com/2019/01/31/the-odd-reason-apple-kill...

Late in this article, you can see Facebook's statement that all minors who participated did so with signed parental consent forms:

https://gizmodo.com/facebook-is-paying-teens-to-install-a-re...

Facebook's statement: "Key facts about this market research program are being ignored. Despite early reports, there was nothing ‘secret’ about this; it was literally called the Facebook Research App. It wasn’t ‘spying’ as all of the people who signed up to participate went through a clear on-boarding process asking for their permission and were paid to participate. Finally, less than 5 percent of the people who chose to participate in this market research program were teens. All of them with signed parental consent forms."