Not sure how far along you are in your planning, and this is a late suggestion, but consider Turks and Caicos. Have gone there several times, most recently with my wife and 1 year old daughter. We stayed at the Royal West Indies resort this year, Ocean Club last year, which are two of the many resorts on Grace Bay. An AWESOME place for divers and snorkelers alike. I have been to the Keys several times, don't remember much in the way of snorkeling, I do know that people snorkel in Pennekamp. But here is what I like about Turks - especially as compared to the Keys.
1) Spectacularly beautiful beach, right on the property, you can walk for miles on it. No real beaches in the Keys.
2) The resort (Royal West Indies) was really lovely. Amazing landscaping, great pools, very kid friendly but with some quiet areas for adults.
3) These resorts are actually condos, so we were able to rent a really nice suite for three adults and the baby with two bedrooms, two bathrooms, two kitchens, and two really nice patios. Not too expensive, either.
4) GREAT diving.
5) Some of the best snorkeling that I have ever seen, especially at the reef off of the Coral Garden resort, with a wonderful little bar/restaurant right there called "Somewhere". You can take the whole family, park yourself on the beach or at the bar, and snorkel a bit, sunbathe a bit. If you stay at Coral Gardens, you have the pool (and a dive shop) right there. In the Keys, what snorkeling there is requires a boat ride, so you basically have to commit to (and pay for) an afternoon of snorkeling, and if anyone wants to take a break, they have to sit on the boat. Often not so comfortable. At turks, you snorkel all you want for free.
6) Direct flights from NYC (not sure where you are coming from... Buffalo?)
7) Lots of non-diving stuff to do that seemed a bit easier than in the Keys (sailing, other types of boating, windsurfing, etc..). For example, at our resort, you could take a sailboat right off the beach, a few steps from your room.
Nothing wrong with the Keys, don't get me wrong. It's also great diving, I'm running another trip there this year for my club. But the reefs are pretty far from short, the best diving is the deeper stuff (the wrecks), and in my opinion, the shallow reefs off the Keys aren't really as nice as what is available in Turks.