[lachlanjc]

Working on projects with people you meet/know isn’t illegal. Getting a real job would be, but not this :)

[smt88]

If those people are in a company and that company benefits from your work, they could still be breaking laws related to internships and child labor.

Unpaid internships are illegal except under some very restrictive conditions.

That said, these things don't seem to make it to court, so you're probably not risking anything by doing them.