Getting warmer, but nope, these are not what the mystery AU will be!
I might do something in the future with only Dean shrinking down being found by a kid. The interactions would be fun, and seeing how Sam comes in just as fun. Big-little brother to the rescue! Or something. But nothing on the table just yet.
A kid finding both shrunken brothers… I’m not going to say anything more than that might come up in Brothers Lost. Don’t want to spoil everything, after all. 😉