Don't forget the things to be done before you go!!! When my children were young and we were out shopping or whatever, I would ask them to point to the person they would go to for help if they couldn't find me. I would then ask them to tell me why they chose that person. I could then praise them for a good choice or direct them to someone who would be a better choice and why.
We also have code words for each child. They know they are not to go with anyone, even someone they know, unless this person knows our code word. This is to keep them from going with someone who may say, "Your mom is right over there and asked me to come get you." or something along those lines.
These things are best done before you leave not when the kiddos are overstimulated by everything WDW has to offer.