I'd see some evidence.
Neither are particularly good behaviors, but as a "computer guy" I think your public-facing API (science fair admissions) should validate its inputs. There are people out there who send know malicious requests to endpoints, you know.
Instead of blaming an underage student I'd reevaluate all of their prior nominations. Chances of dragons being there.
> The child is nothing to be blamed for, it is a 100% problem of the organizers.
This is what I disagree with. A 17 year old is not an innocent child that mustn't be blamed. At this age (and already earlier too) there has to be real consequences for plagiarism, proportionate to the case.
Plagiarize coursework? Fail the course. Cheat in final exams? Fail the exams and retake the year. And so on.
If that's not his first participation then the previous ones should also be reevaluated.
But that doesn't have much point since he's growing out of them already. And I don't think it's fair to pursue him further (other than existing bad publicity) since people do stupid things all the time and the idea of limited liability exists for a reason.