It hasn't 'now' become a thing originally from adult fetishes.
30 odd years ago kids were into this stuff and many of them are now adults into this stuff. Most have no fetish connection with it.
How do I know? Been there, seen it, taken part in some of it as a teen, still know lots of adults who were kids at the time etc.
It actually is entirely harmless. Discouraging kids from being allowed to dress with ears and a tail when they're expressing themselves and enjoying something harmless is ridiculous.
The only thing which needs watching is if they end up on the kind of social media they shouldn't have access to in the first place, where they might join groups for the minority of adults who do take it further go.
It's no different to how many of us love to dress up or cosplay for fun and because we are into fandoms or enjoy making the outfits, but you'll always get people who like to dress as medical staff, candystripers and school girls etc for sexual role play.
I mean, have you ever heard of sploshing? Go have a Google. You all going to ban cakes and sweets and midnight feasts at kids slumber parties? Of course not.