A.M.
Marco Island is about a 2 and a half hour drive from Miami at the southern most tip of FLorida. I believe its known for having great fly fishing. THere are over 50 locally owned and operated restaurants. Activities offered range from paddle boats, jetskiing, power and sail boats, charters, parasailing, biking, watching dolphins play,and shopping. Just a few minutes over the Judge Jolley Bridge, you will find Prime Outlets Mall with stores such as Liz Claiborne,Canon, Coach, Ann Klein,...
I imagine you are staying at the resort where the couple is getting married? If you can get another couple to stay with you so you guys can split it, I suggest staying somewhere like here once the wedding part of the trip is over:
http://www.vrbo.com/167495
Its much more romantic and "homey" than a hotel. You can stock the fridge,barbeque at night,walk straight out the front door to Tigertail Beach. No messing with elevators.
I'd rent some bikes and explore Marco Island. Get one of those bikes that have that attachment for children to sit in.
Naples is about 20 min away. Key West may be a fun day trip as well.
The owners can recommend restaurants as well as babysitting services should you decide to go out for the evening.