Wayne, there is SO much to do in Miami. Since you are coming with family, I will suggest stuff that hopefully will appeal to all ages.
Of course on my list would be
Parrot Jungle --
http://www.parrotjungle.com/
Art Deco historic district -- An area of Miami Beach noted for its concentration of over 800 Art Deco buildings all within one square mile. You can join the walking tour which takes you past the white- and pastel-colored stucco buildings beautifully restored to their former splendor thanks to the Miami Design Preservation League.
Amsterdam Palace (Versace Mansion) -- Gianni Versace was killed at this spot. Since then it has become a tourist attraction.
Lincoln Road -- A pedestrian walkway with entertainment, shopping, shows and great places to eat.
South Beach --
http://www.visitsouthbeachonline.com/ -- People watching is a great pastime in Miami's South Beach, which draws celebrities and beautiful people in skimpy swim attire to see and be seen. The wide and fine, white sand-covered beaches are popular spots for fashion photo shoots, so you're sure to see models. The area is known for its hip clubs and wild nightlife as well as numerous excellent restaurants.
Bayfront Park --
http://www.bayfrontparkmiami.com/
Miami Zoo
Not sure if you are renting a car but I would also make it point to visit Fort Lauderdale beach area --
http://www.sunny.org/visitors/index.cfm (north of Miami 20-30 min), Coconut Grove area (about 15 min south of South Beach), or even the Keys --
http://www.fla-keys.com (top of the keys is approx 1 hr to Key Largo and 2.5 - 3 hours to Key West -- in between the two you have Islamorada, Marathon, Big Pine/Lower Keys and then Key west ... in that order)
Man, I can keep going but I don't want to point out things that may not be of interest to you. These are just some things off the top of my head that I have told friends in the past that were visiting and they all loved it. The links I posted have even more attractions and descriptions listed.
Just be sure to bring some good walking shoes. You will probably spend allot of time walking and sight-seeing as opposed to driving.
Hope this gets you started.
Curtis