I'd be interested to hear from parents who allow this, and encourage it by the purchasing of items, as to how they think there's not something troubling going on?
Let's take away the blatant fetishism and issues with the furry community for a moment. 11+ children wearing tails and pretending to be animals either for a vast part of their day at home, or in public? Do you really think that's a normal thing for this age?
I'm not saying children should be growing up too fast or that we should be encouraging it. But this is abnormal behaviour for that age-group. When I was 11 I'd started my periods. My peers had outgrown dolls (at least they said they had), and we were moving into that strange gap between young childhood and adolescence.
For a brief while at university I tutored as a part time job. The 11 year olds were far beyond this sort of stage. It's a regression. If you had a new baby and an older sibling suddenly began to pretend to be a baby too, you'd think "ah, this is in response to the changes. Perhaps I'd better spend more time with them, or make sure they're involved, blahblahblah, etc."
Yet this is okay? If my child started doing this, I'd be concerned. Deeply. As for ASD children doing it, I'd probably be more concerned in case it left them in vulnerable situations they may not feel able to navigate.
It's not cute and it's not normal, and parents really need to take off the blinkers and get with it.