Found: Stiles and others de-aged due to spell/curse?
TW for possible child SA or discussion of child SA.
I could be misremembering this completely, but here's what I've got: I think some of the pack are de-aged by a witch's spell or something. I think this happens while in the preserve. I think the idea was for them to be aged back to the age they were when they lost their virginity. There might have been some joking around going on when everyone realizes this, only then Stiles steps out of the woods and he's just a little kid. I don't have any really clear details other than I just have a feeling I've read something like this before and that it was from this fandom. I'm not sure if there was a pairing or if it was gen.
Found: https://archiveofourown.org/works/29907870