First of all, let me comment that the wording in that quote did not anticipate their possible extraction to a general rule. While I think there may well be rule-worthy stuff in that line of reasoning, wording such as "influential adults" is probably not fit for FAQ, but rather just adds another layer of subjectivity.
What I'm trying to get at is the intent parameter, that I think lies at the very core of scientific skepticism. We don't have a problem that Tolkien writes about elves as though they existed, because he never explicitly claims that his work is anything but fiction. This differentiates from when Hubbard writes about Xenu. We don't have a problem that Derren Brown and James Randi perform their stunning tricks, because they never call them anything but tricks. This differentiates from the psychichs who use the same stunts to claim supernatural powers.
We currently exonerate Randi and Tolkien by referring to the claims they are (or, critically, aren't) making, but I think this reliance upon claims is an abstraction of a more fundamental rule, which we need to identify. It seems to me that no sound skeptic would make a big fuzz about toothfairy claims, and I think that this is by means of the same mechanism that motivate us to accept Randi and Tolkien. But if that is the case, then the claim had nothing to do with it, it was merely a somewhat strong correlate of another parameter, which is the true differentiator, because in the toothfairy example there are truth claims (made by parents), but we still don't really object to them.
I think it would be desirable if we could get to this parameter, and use that as a rule, rather than something that often correlates with that parameter.
If some random lunatic happens to believe in something new that they've conjured themselves just now, then that may also be a non-issue to a lot of skeptics. I suspect that this is by the same unnamed reasoning. This leads me to thinking that the claim should be made by a legally competent adult in order to be a valid subject of skepticism, and further, that this adult should somehow intend for the listener to adhere to that belief as they grow up.
It would be compelling to say that the one advancing the claim should believe in it themselves, but in that case we'd probably disqualify psychics whose elaborate reading techniques renders them unlikely to believe in their own claims.
So what we want to get at is the claims that are obviously made just for the entertainment of it. Perhaps the "apparently in good faith" clause is sufficient coverage of this. In that case, is "legally competent adult" ubiquitous enough and sufficiently specific? If so, then my answer is yes, questions should be able to reference that the claim is being made by legally competent adults, apparently in good faith.