This has been discussed on these boards before, you might want to SEARCH for previous threads.
FRS (Family Radio Service) radios don't need a license.
They have a range of up to a mile or two and are the type recommended for this use. Some units have over 30 "channels" (although many are really just digital "sub-channels" of the actual frequency in use) to choose from for individual use.
The PROBLEM is that at WDW there may be hundreds of them in use at the same theme park. Finding a clear channel to communicate may be a big problem.
Many have decided the best way to talk when you really NEED to is to use standard cellular phones. They may cost more to use under RAOM conditions, but they WILL work when other types of wireless devices won't be reliable.