when the ocean is smooth, you can anchor there but being open waters it's not ideal for the kids. Biscayne bay is indeed the place you want to go...
If you're in FTL, is mostly all no wake to miami, so you're better popping out off Port Everglades and come back in either at Gov Cut or Cape Florida. (keep in mind that Gov Cut is a security zone so once in the inlet, you must get on the south side of the commercial port, by fisher island towards the River and ICW
in biscayne bay you have many good spots starting with the anchorage on the West side of Key Biscayne (off KBYC), just north of the sand bar at the SW tip.
No Name Harbor, by cape florida, is nice toom, although crowded on week ends but great for kids because of the park (crandon beach is within walking distance)
12miles south is elliott Key which has the clearest water and best anchorage on this side of the stream. with almost 6' you can come in fairly close, up to around where the idle speed markers are.
with 6' Boca Chita is too shallow but you can dinghy in there from Eliott.
Pumplin Key is ok but the water is nicer at eliott.
on the outside there are many moorings where you can tie up to snorkel, some great spots including the Christ of the Ocean ust north of KL.
nearly 6' will be too a little deep to stay on the inside of the keys, depending on winds and tide.
I have a number of placemarks covering Biscayne Bay and the Keys in Google earth. they can viewed in Gloogle Maps in your browser http://maps.google.com/maps?f=q&hl=e...om/hattcam.kmz
or download the Google Earth file http://www.sandbarhopper.com/hattcam.kmz
hope this helps!
Welcome to South Florida and wonderful Biscayne Bay!