We didn't go in September, but DID go in March last year, during the early end of Spring Break. To give you an idea of crowds, Easywdw listed the whole week as a 7 for the WDW parks. We were able to pretty easily get done with almost everything in one day. My one piece of advice is to go to the back of the park to the driving/boating schools first if your kids want to do those. That was the only area we had any real wait!