dman:
I think I'm going to try to find out from Royal Carribbean who they book with in each stop and contact those operators directly.
In case you haven't found out yet:
http://www.redsailcayman.com/gc_cruise.html
I second the option of shorediving the Turtle Reef site. It's called Turtle Reef though, not Turtle Farm - that's something else entirely. It's Divetech's second location and is probably the closest point to the Wall if you're up for a swim. If not, there's a mini-wall 40yds offshore that's really a great dive in itself - full of coral and fish and it bottoms out in the sand at about 65'. Generally see Tarpon hovering in the shadows, a good chance for Turtles(obviously) and we saw Eagle Rays go flying overhead. For even more fun, they rent Apollo scooters.
Probably a 20min cab ride each way though, it's pretty far north.
http://www.divetech.com/index.htm
If you want to stay near town, I'd recommend Sunset House over Eden Rock. It's just a 2 min. ride south of the Cruise port, the diving is better off their "cement ocean pool", there's the mermaid Amphitrite in 50' for photo ops and another small wreck farther out. And it's deeper past that - not sure how old your "kids" are.
There's also a great, inexpensive bar/grill there, My Bar, it's the divers hangout on Cayman. And the Cathy Church photo gallery is in the basement of the main house. Full diveshop on site, they rent anything you'd need.
Eden Rock, while an easy entry, is pretty tired and beat up. Mostly because they do get thousands of cruise divers yearly. And their reef ends in sand flats in about 45' of water, beyond that there was a jetski riding area and your ship(and others) is 1/2mi. offshore past that so you can't go out there. Not that there's much to see, just a lot of junk dropped off the ships.
Of all the shoredives listed above that we did, Eden Rock is the only one we thought was disappointing. They do have good facilities and staff and they rent everything also.