Hi Swmchx - you will probably enjoy having a cart during your stay at Calm Caye and Coco Caye Villas. You will need two carts to carry all of your group if you are going someplace together. (I do not own a a golf-cart company, nor do I have any close associations with anbody who does) You would probably use the cart mostly for getting to dinner spots - Caliente, Rendezvous, Rojo, Mambo, Capricorn. Going to town on the cart can be fun if the roads are in better shape than now (and in November they will probably be ok) - today the flooding rains have turned the road into an obstacle course.
Depending on the kids, you may want to rent bikes for daytime excursions to town and to other spots up and down the coast - it's a nice ride along the beach, and you can probably get to town faster on a bike than in a cart.