These are bars. It is a nightclub atmophere (well, there is the Comedy Club and the Adverturers Club). The music is loud, people drink, they dress in "clubbing" clothes, jello shots are sold on the street. Disney does allow people younger than 18 admission to the Island if accompanied by a parent, although some of the clubs don't let you in if you are under 21. Kids are not common. Don't be surprised if you get dirty looks.
My understanding (I haven't been since I had my own children) is that it is pretty tame from opening until 9:00 or so. But most of the dance clubs don't even open until 8:00 or 9:00.
As to your daughter enjoying it, that depends on your daughter.
(I've always kind of wanted Disney to take Atlantic Dance on the Boardwalk - which has always had a identity problem - and turn it into a family dance location).