Miami seaquarium is OK, but honestly not all that great. The place is a little rundown.
Parrot Jungle island and Monkey Jungle island are both very nice and I hear great things about them. Miami childrens museum would be fun. What dates are you here? there is some fun local festivals depending when you are here.
Key west wont be worth it. Too long a drive with beaches just as good here in Miami.
The Everglades Gator Farm is much cheaper than other swamp boat rides and offers a gator show, snake show, and boat ride. Yet the whole place can be done in 2 hours to make it easy.,
Butterfly World is in Ft. Lauderdale and is a great place! I love it. A huge butterfly sanctuary with thousands of butterflies fluttering about. There are also birds and bugs to see. Wanna-do city in Ft. Laudersale is also tons of fun for the younger set.
Hubby and I like to go to Bayside Mall down by the port and take the scenic boat tour of some of the celebrity homes around there. Bayside is also a cute place to walk around and grab some food and souvenirs.