I've been to WDW many times with kids as the only adult, and I have a bathroom method that you might want to try. You can even test it out in your hometown--someplace that has multiple stalls in the bathrooms. I put the child in the stall and have them lock the door. They must stay in there until they see my shoes under the door before coming out. I always choose stalls that are next to each other, or at least nearby. That way we get our own stalls and I don't have to worry about losing track of the child. Sometimes a child gets too big to share a stall, but not old enough to be on their own at the sink area. This method has always worked perfectly for me.