My family and I just got back from a week at the Moorings Village in Islamorada, Florida (Upper Keys--about 1.5 hours drive from Miami). The Moorings is great if you're looking for a quiet, laid-back vacation spot. The resort features a small number of houses and cottages, a private beach, lap pool, small fitness center, and spa.
The Moorings is not specifically geared towards kids, but the majority of the guests there during our stay had small children (including us). It's great for kids because everything is very close by--the pool and beach are no more than a 3-minute walk from anywhere in the resort (a very good feature for those with small kids with small bladders!). Plus the water is very shallow near the shore, and there are lots of palm trees to provide shade. Having a house with a full kitchen was a nice feature, and you can ask them for a grill if you want to barbeque. They also provided us with a pack-and-play for our daughter and a baby gate to block the stairs. There's a TV and VCR, and a list of babysitters in the area. Housekeeping services are not included, but you can arrange to have them come in and clean if you'd like (we didn't). The houses also have washer/dryer and dishwasher.
However, the one thing to consider if you want to bring your kids is that the Moorings is a very quiet place. We have a 20-month old and a three-and-a-half year old, and while they are normally well-behaved, I've learned that everything can change when you're in a new, strange place! The stress of dealing with with a tantrum-throwing kid is worse when you're desperate to keep them quiet (and of course they can always sense when your back's against the wall!). This trip taught me to have very *low* expectations for traveling with small children. In retrospect, I might have tried a "dry run" with the kids at a place that's less expensive because I don't feel that I was able to get my money's worth due to the kids' behavior.
In short, we chose the Moorings because we wanted a low-key place, and it certainly fit the bill in that regard. However, next time we might go someplace that offers day care!