I've been to various islands (Velidhu/Coco Beach/Makunududu) and I've seen a few babies. I've not seen toddlers, but these weren't "family islands".
The babies I saw would tend to be out early in the morning...and reappear on the beach after about 4pm. You are on the equator, the sand is brilliant white.
I think you will definitely need to overplan this trip. I'd be worried about how easy it might be for a toddler to get out of a villa's patio doors and go wandering into a plunge pool..fall off a pier etc. You might be super-vigilant, but would the siblings remember?
If your husband is a diver, figure out whether he wants to dive all the time, or would he prefer the joy of swimming/walking out to the end of a pier to a house reef (where he might potentially night dive etc). is he dreaming of this trip to see Manta or Sharks etc. Then start working back from that and price continually! I love house reefs (as I probably need to refresh my PADI before I dive again).
I suspect that 14 & 8 year olds eat like horses, with iceceam addictions, so it might be worth restricting yourself to islands with all-inclusive options?
DD (7) is a massive water baby and we're getting close to looking at prices.....I wouldn't have considered it before (though dragged her over to Oz and the Caribbean before school) because there really isn't too much to do if you hate reading/swimming/computer games.
We'd now happily spend hours on the beach swimming/snorkelling/playing but I'm not sure how that works with 2 very active boys and a toddler if your husband is hoping to sneak off?