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Could be Glamour Failure?
^ Nah, this is more like using "kids have vivid imaginations" as an excuse.
I've actually seen it before in a different context, where the heroes were accusing the villains of their actions, and they kept pulling the "wild imaginations" card to make others less trusting of what the (teenaged) heroes were claiming.
Current Project: Incorruptible Pure Pureness
Reading the title makes me think of Youth Is Wasted on the Dumb in general
We can never truly eradicate the coronavirus, but we can suppress its threat like influenza
bump?
If there's a book you want to read, but it hasn't been written yet, then you must write it. Toni Morrison
Nah, that’s ignoring important stuff.
If there's a book you want to read, but it hasn't been written yet, then you must write it. Toni Morrison
Cassandra Truth is the general idea of revealing the truth and everyone around you just doesn't believe you. But I don't think we have anything specifically about "Oh my, what an imagination!" as an excuse to dismiss what the truth-teller says.
I didn't write any of that.
Probably a case of Weirdness Censor as an Exploited Trope, taking advantage of the perception of any fictional kid as Just a Kid (and thus segueing into Not Now, Kiddo and further exploiting Adults Are Useless) to deliberately trip people's censors.
When a young character blurts out a fact of the masquerade and the older character says this phrase or a variation.