My DH and I were at PI in 1996. We were in WDW for an adults only trip (two DD's were with aunt/uncle/grandma)
OK....now keep in mind, the only drinking DH and I do is about 4 times a year we have A glass of wine with dinner. Yes, you could say we are not the "partying" kind, (I've never understood how getting drunk and using foul language/body language is a definition of "fun" anyway) but I digress.............
We were all set on having a great evening, though I must admit, I didn't know a whole lot about the place. We went in, had an appetizer at one of the clubs, no drinks and went back on the street to see if anything interested us. This was probably around 9:00pm.
We saw pretty much the sort of things that have already been described in this thread. Not exactly kid friendly. WE didn't even want to stay there! But like I said, we are not the night club type. I would NEVER want my children to see that stuff. Maybe my kids are sheltered, at least I HOPE they are.
The clubs at PI should be adult only just like any other club. (at least I don't THINK you can bring your stroller into a NYC nightclub

)
On a high note...................after DH and I decided that PI wasn't for us, we saw the movie theater. I would NEVER think to go to a movie on vacation, but this night was meant for PI and it was now an "open" night. We saw "That Thing You Do" and LOVED it!! It is still one of our favorite movies. The night ended up being a "memory maker" for us. Everytime we watch the movie, we think, "oh, that was when we were at WDW for our second honeymoon!"