You didn't specify if you're interested in anything other than warm water diving. My guess is probably not because only a small percentage of divers do that sort of thing, and most younger divers aren't going to want to deal with heavy wetsuits or drysuits, thick gloves and the additional gear that is required to dive in dark, low visibility water oftentimes with current. So if that's the case, your only real open water diving is going to be in Florida, and as the other poster said, in order to stay within the depths of the younger diver's certification, it's going to mainly be the Florida Keys.
There are several springs and rivers that are available to dive in Central Florida but you're going to need heavier exposure protection.
As far as Epcot Dive Quest goes, I did it once, and sure just like any other aquarium dive it can be fun as a "do it once" sort of thing but don't get your expectations up too high, it's probably not as great as you're thinking it's going to be.