I can't speak for the age, but my 9 year old is a girl and she loved it. 4 seems a little young for the late night. My daughter would have been fine at 4, but not my son. I don't think he would have been able to stay up that late at age 4.
I think we had to be at the contemporary at 7:45 and we got back to our resort (Boardwalk) around midnight.