Duck tour,Parrot Jungle, art deco buildings, mall, alligator alley boat ride, cinema, beach, watching cruise ships, or drive up to Fort lauderdale and cruise the waterways with a daily pass.
I would avoid the beach hotels as the resort fees and parking charges are horrendous...have a look at the 2 bed villa at Marriott's Villas at Doral, about £100pn, or we like to stay at Crowne Plaza at sawgrass mills for the outlet mall and restaurants (wait for the rates to drop to $100 a night first).
This year in August we got an amazing rate to stay at the fairmont turnberrry isle which was exquisite and has a lazy river which the kids loved but valet only and resort fee adds £50 a night to the $99 rate.