I would recommend the Florida Keys. Lots of quirky little attractions to check out (bird rescue center, turtle rescue, monkey jungle, even the gift shops are fun for kids). You can snorkel right from the beach (take turns with your spouse). You could take your toddler on a little kayak ride by the beach. Kids love the beach. Plenty of casual restaurants.

We did Mexico (Riviera Maya), Jamaica and Captiva (FL) at that age and had a great time. I did find it a difficult age for plane travel - so definitely do non-stop.