As the mother of a 8yo with ADHD, we are experts at the whole Lost Child thing.
Some of the things we have learned:
1. [ QUOTE ]
while it seems that more adults=more supervision, that may not be the case
[/ QUOTE ] This has a major flaw. More adults can also mean "I thought he was with you". This happened to us in the big store in Animal Kingdom. DS was 4yo at the time and had 5 adults watching him. So, of course, he wandered out one of the many entrances, without any of us. Security found him and stayed in the area with him.
2. For a wanderer, tell them to keep one of the adults from getting lost: they're more likely to stay with whichever one you name.
3. You can get a name tag at Guest Services at any of the parks. You fill it in with the necessary information and pin it to the tag in the back of the child's shirt. Hanging inside, it isn't obvious to everyone walking past. Make sure the child knows it's there and why. (Better than relying on memory; an upset child doesn't have much.)
4. If you have lots of trouble with this, you can always do what we've done: tell the child that Disney Security only gives you three strikes and then you're banned from the parks.