Couple of random thoughts. First, I don't see a specific problem with some adult interaction with kids. But trusting your instincts and protecting kids from predators is just good sense.
Unrelated (but relevant to the thread) there was a thread a long time ago where a kid was, I think, 15 and competing in a BJJ adult white belt division. He was grappling with another kid. technically an adult of something like 18. Anyway, there was an accident and he ended up breaking his neck. A lot of controversy at the time about whether or not he should have been competing as an adult. Point then and now is that we have age divisions for a reason, and as a general rule, those reasons make sense for most people. But exceptions occur, and I think that's a good thing, not a bad one.
Edit: I found the thread from 2015... won't link to it here but it's out there to find, but it was a 15 year old and a 19 year old, and they were in the blue belt division.