I worked for Disney for 7 years and we were told that it was a urban legend and that they have a plan in place anything does happen but that most of the time it's parents being seperated from a wandering todler ect.
Think about how busy it is there, how long it takes to cut a child's hair and colour it. You cant tell me that no one would come into that washroom during that time.
Kids get lost all the time, there are plans in place in most larger retailers too.. Its called Code Adam. The stores go into lockdown if after 10 minutes the child isnt found. Gap Inc stores and
Walmart use it all the time. I can tell you that 99% of the time the child wandered off to look at something and that's when we have had to use Code Adam.