How should I, legally, deal with a minor as a contributor?

I mean, I wouldn't consider it if I hadn't worked with his dad for 5 years. It's not like I'm actually hiring, but yeah.

I was aware of those 3 rules, and was really looking for the citation on 3 earlier. I was thinking about paying him, I can afford a few hours of minimum wage, and if I think I can't I can always stop it, but even then I'm not 100% certain what I'd need to do for that. Do I actually need to file for incorporation of some kind? at this point I'd probably just go sole proprietorship if I have to. Then I'd guess I'd need to either have him do a 1099 or W2 of which I might need to contract out to a HR company to deal with some of it, especially because of the across state lines stuff. I honestly only vaguely remember my employment around his age.

I just want to ensure I don't somehow end up with them owning half the startup if it ever goes somewhere by virtue of a later lawsuit.

For some reason this made me chuckle. You indeed are a minor :D

The problem OP is facing is not that s/he is unable to treat the contributor as adult. Which probably s/he is. The problem is the law does not treat minors as adults. There are reasons for this. Minors are exploited in all sorts of ways. Infact, interns(even adult ones) are treated badly. Once I was working for a company(a world leader) in the UK. A new intern joined. Next day he goes around everyones desk in the team as starts asking if they would like tea or coffee! And everyone was telling them their preference. He came to me as asked this question. This was new to me. I asked him, is this his assigned task? Who assigned him this responsibility to bring tea/coffee to everyone at thier desk? He looked shocked and confused. I said to him that I would be happy he if rather come to me with a work related problem. He did not say a word and went to the company kitchen and bought everyone else their preferred drink! This is how interns are treated. Think what will happen to minors if there was no law.

Disguising work on a startup as "open source contributions" would be fraud. The type of fraud that might lead to violations of child labor laws with hefty fines particularly since the original poster is fully aware of the status of the out of state minor making it a "willful violation".