If we were talking about a deserted local park, or a shopping mall, or a library, or a department store - places that ARE open to the public where anybody can walk in and use the restroom, then I could understand taking a 9 year old boy into the ladies room.
But we're talking about Disney World. And I don't say it that way because Disney is sanitized or simply because it carries the Disney name, and therefore must be safe. I'm talking about a place that attracts probably THE most families of any place on earth. Whenever I've gone to the bathrooms at Disney World, there is ALWAYS a dad and his son in there. Usually, SEVERAL sets of fathers and sons. I can almost guarantee you that if anyone tried anything with your son, there would be several fathers ready to jump any loon who tried anything with a child who wasn't theirs. Not to mention that anybody that preys on children is going to have to pay $67 (plus tax) to get in. Anybody that has that kind of money to spend on a "fix" has probably been featured on the Chris Hansen "To Catch A Predator" series on NBC.
As long as I can remember (and I remember things from when I was 4 years old) - I don't EVER remember being forced to go into the ladies room with my mother. And if I did - well, quite frankly, I would have been HUMILIATED.