Grand Cayman might be an option. There are a variety of both deep and shallow dives that would accommodate your group. Additionally since there's 6(7?) of you diving, with some of the smaller diveops you could likely pick shallower dive sites if desired since they only take 6-8 divers max, so you'd "own" the boat. A typical 2-tank dive on Cayman goes deep to the wall (60+-90' or more) on the 1st dive typically followed by a shallow 2nd dive. And the reef/wall often starts at 60' so above that your junior divers wouldn't have much to do.
Three dives we did off Grand Cayman's West side were Peter's Reef (48'), Aquarium - excellent site with a lot of fishlife (48') and Governor's Reef (49') You'd have to check with a diveop but as I recall there were even shallower areas at each site.
And there's decent shallow shorediving at a couple of locations. One is Eden Rock/Devils Grotto. Frankly the reef isn't in the best of shape because they get a lot of cruise ship traffic being located downtown but the upside is that the swimthroughs start at 25' and I don't think the whole divesite much exceeds 40'. Out past that the cruiseships anchor so not much out there anyway. I show the dive in my log at 38' and I was laying on the sand under a coral outcropping to get that. At that depth, we had a lot of air, also they rent 100's so we must've toured the whole site twice. It's a pretty entertaining dive with some small overheads, esp. at Devils Grotto to the south.
The Cayman Islands Best Shore Diving off our dive shop
Another option is Sunset House, their reef starts in 15-20' of water just offshore or shallower. And has multiple levels leading down to the Mermaid Statue (53' standing on the base) Again maybe not the best dive but I enjoyed playing around with the fish in the shallows (15' or so) on my way back in. Easy entry too, they have a salt-water "pool" that's open on one side to the ocean. Most of the Cayman shore dives have some sort of ladder or other easy access into the water.
And of course there's Stingray City, the most fun the kids (and you) will have in 15' of water. It doesn't get any deeper there, the kids will get mobbed by the rays and likely get to see the resident Moray up close. You should watch the smaller ones though the Rays are pretty powerful, I've seen masks get bumped hard enough to flood. At the time that we were there, no one had
ever been stung, sometimes you get "kissed" by a Stingray though. Since they don't really have teeth, it's more like a hickey that your kids will have long enough for show & tell at school...lol.
On the surface it's a pleasant island. Seven Mile Beach really is about that long, pure white sand all the way along it. No shorediving in that area though as it is a great beach. There's a waterpark now - Boatswains Beach - part of it is the old Turtle Farm. When we were there, they were pretty open about the turtles being made into products so might check if that's still the case before you take the kids. And there's a butterfly farm. Shopping downtown and around West Bay. When the cruiseships are in town, you want to be elsewhere. Since you're a larger group, there are some 3-4BR condos available for rent as well as every class of resort. Most sit right on/near the beach also. First week of December is usually Jazzfest also.
Cayman's kind of pricey though. But I thought Toronto was even pricier.
Pretty much everything you need to know:
www.caymanislands.ky
