They have to be careful about that. Most high school sports associations ban any kind of payments to athletes, including prize money. One of my kids was in running and if he entered any kind of non-school race he had to get a waiver from the state and also decline any prizes (trophies, medals, ribbons, etc. were OK). I think it may also be possible for stuff like that to impact college/NCAA eligibility, i.e. once you have been paid or earned money from your sport, you are never considered an "amateur" again.

While that's a practical complication, it's one that has a huge number of holes in it—thus my mention of racing in particular, which is often overlooked as a "sport" despite the physical demands it can put on drivers.

More broadly, it points out just how incoherent the demand that some athletes remain "amateur" is, when "amateur" is just used as a proxy for "unpaid": there's nothing noteworthy about a teenage driver winning a cash prize for a small-time race, and nobody in the pro racing world is going to say that they're not an "amateur" driver just because they got money for racing once.

Yes, this is part of the horribleness of the NCAA. I have never heard of someone getting kicked off their school newspaper because they wrote a paid article for someone else. Why shouldn’t athletes be the same?