Sorry OP I still find you churlish. You may have a point if its "kids corner" but that is it. It strikes me as a rather odd attitude.
Calling something "a childish activity" is not the same as saying "children enjoy it". Plenty of activities are enjoyed by children and adults alike. If your argument is that adults who enjoy petting zoos have "failed to grow up", then logically you'd have to apply the same standard to: zoos, aquariums. Lego, model railways, theme parks, Disney films, Harry Potter, comic conventions, colouring books, & feeding ducks
Most adults draw the line wherever their own interests happen to lie. I'd argue that one mark of maturity is being comfortable enough to enjoy things without worrying whether someone else thinks they're "age appropriate". Children often worry about looking grown up. Secure adults tend to be less bothered. There's also a difference between: enjoying a petting farm because you like animals, and wanting to be treated like a child. An adult having a cuddle with a rabbit isn't pretending to be six years old. They're interacting with an animal. The rabbit doesn't care whether the person is 8, 18 or 80.
Personally I don't go to petting zoos because I kidnap passing dogs for cuddles and I get lots of them every day. I find it very therapeutic and restful. If that makes me childish - tough, I can live without your approval.
What I find interesting is that many people who make the "adults acting like kids" argument are perfectly happy spending an afternoon: watching football, collecting memorabilia, gaming, queueing for the latest Marvel film, discussing horse racing form, building a railway layout in the shed, all of which could equally be dismissed as "childish" if someone wanted to be uncharitable.
Personally, I think there's a great deal of joy lost when adults decide that affection for animals, curiosity, playfulness and simple pleasures are things to be outgrown. I'm in my 60's and on the cuddly side but last year I frightened the living daylights out of a group of parents waiting at the bottom of a tunnel slide attached to a castle when I shot out, because they were expecting a kid and they all cracked out laughing. As C.S. Lewis famously put it "When I became a man I put away childish things, including the fear of childishness."
That, to me, is a much more mature outlook than worrying whether stroking an alpaca looks grown-up enough. 🦙😊