I think they might be more accurately referred to as rip currents. Anywhere you have waves, I would expect rip currents although some areas are a lot more threatening than others. I wrote an article on this for the Kiteboarder a while back:
http://fksa.org/showthread.php?t=9552
They have them all along the eastern Florida coast. They are usually a greater threat in SE Florida for weak swimmers, children, the elderly and less of a problem for strong swimmers particularly those that swim out of them parallel to shore. Most kiters seem to ignore then in our area being strong swimmers with the smart ones wearing impact vests for the odd bad day.
They don't run the downwinders all the time so if one comes up during your visit and you can get away that may be the one for you. Otherwise I would try to get out to Stiltsville if good winds are on. The family could go to the Sea Aquarium, Crandon Park, Bill Baggs State Park or even the atoll-like lagoon at Matheson Hammock while you are offshore. These are all somewhat near where you would board your sea taxi boat. They could even go to South Beach and drop you off.
Most of the Keys contain flat or calmer water and there are a number of readily accessible launches down there. Some rent SUP gear like Whale Harbor (I think) and Smathers Beach in Key West. Some of the kite shops down there rent SUP boards as well. There are grass beds nearshore for snorkeling but the reefs might be more interesting still. Regarding Stiltsville is a unique venue with the stilt buildings, Miami skyline, Cape Florida lighthouse, etc. and if you can fit it in, I would try to do so.
There is an artificial reef very close to shore in Boca Raton off Red Reef Park, the Delray wreck off south Delray about 800 ft. offshore. The reefs are closer to shore and shallower south of Hillsboro Inlet in Pompano however. If there is much wind, these areas may all be chopped up with poor visibility. Taking a snorkel boat to the Florida Reef Tract down in the Keys if conditions are good would be more ideal I think. Key Largo offers some good prospects in that regard.