I did, many, many years ago. Back then, Blue Mountains wasn’t even a national park.
To answer your question, yes a koala came and sat on my lap - we visited a park somewhere, I forget the name but it was a tour. The tour guide reprimanded me for having a koala on me (I told him he came and sat on me) and insisted I remove him because of the dangers of its claws (it never hurt me, not even a scratch btw) I feed him & kangaroos food purchased at the site for them. The animals were super friendly at that park. It was an amazing experience considering all the animals were in the wild.
G'day mate!