Can you pay 13 year olds in $20 gift cards and call them a contractor?

Did they get w2s and 1099s? Did FB did employment authorization verification? Did fb verify that the contracts were in fact signed by authorized guardians? A minor signing a contract has no meaning - so no “employment” contract would be valid.

> A minor signing a contract has no meaning - so no “employment” contract would be valid

This is generally false. Minors generally can make valid contracts, though such contracts are usually voidable by the minor prior to execution. [0]

[0] without otherwise endorsing the site as an authority, the discussion here provides a good general coverage of the issue: https://contracts.uslegal.com/contract-by-a-minor/

No, they were random consumers. That's the whole point of market research.

When you are paid to take a survey, do you magically become an employee of the company conducting the survey?

Facebook was paying 13 year olds to use the app, so that argument isn't really available to them unless they want some pretty significant civil penalties straight from the US Government. (I strongly doubt it'd fly either way, but "we hired underage contractors" really won't.)

13 year olds cannot enter into contracts.

Child labor?