We are going on the 9/28 western with ds7, dd4, dd2, and dd18 months. We too were at first a little nervous about how to handle doing any excursions, but we think we have a lot of things figured out after a fair amount of internet investigation--- and lots of help from these boards.
1. In Key West, we do not plan to book anything. We've learned that you can easily board the Conch Train Tour for less money near the port. We expect that our umbrella strollers will be easier to use there because it is a US city, so sidewalks etc. may be more accessible than in other areas. We did the 4 day cruise with a stop in Nassau when our oldest daughter was 10 months old. The stroller didn't work ANYWHERE!!! We wished we'd had a backpack!!
2. In Grand Cayman, we found a place (we think, still checking) that they do horseback riding on the beach. The best we can tell, we would be away from the ship for only 2 hours, top. We are considering doing this with DH desperately hoping I can get over the idea of leaving the kids on the ship. I'm really not sure I can do it. Anyway, whether or not we do that we don't plan to book any Disney excursions. For a family of our size, the prices really add up!!!
We did find out you can do the glassbottom boats, nautilus undersea explorer, etc. on your own close to the port. I also learned you can rent a car quite cheaply there--- ah! A use for the car seats (though tendering with car seats and four kids? Oh my goodness!). If we do this, we can tailor our plans to the kids mood that day--- turtle farm? Seven mile beach? etc.
I also contacted Captain Marvin's. They welcome infants and toddlers on their stingray city excursions. We were going to do this, but dd4 looked at pictures and thought it looked to scary for her. She does get easily overwhelmed, so we tend to believe her when she says that!!
3. In Cozumel--- the day we are most excited about-- we are planning to go to Chakanaab. Myself, dd4 and ds7 will do the Disney excursion for the Dolphin Encounter, using Disney transportation. DH, and DD2 and DD 1 will take a cab to the park and we will meet there. Chakannab is supposed to be a very nice park. It has protected beaches, a jungle to walk through, AND an infant/toddler swimming pool area. There is also a sea lion show and wild bird show. I think entrance to the park is $10 for those 7 and older, free for those who are younger. Also, even though you must be 4yo to do the dolphin encounter, those not participating can stand on the platforms and watch.
I laughed reading the posts about packing food. When we went with DD4 several years ago, we had a HUGE duffle bag that was terribly heavily, jam packed with food!!! Also, she was on formula at that time and could ONLY tolerate Alumentum, which at that time came only in the premixed tall cans. HEAVY!!! It was nice to have the empty back at the end of our vacation to ship all our new finds home in.
The crew made a tremendous fuss over dd, and were so helfpul in the dining rooms. One of the "classic" Disney moments was when the main course came while DH was holding a very animated DD. (We requested late seating, put ds then 3 in the clubs, and then or dd was usually sleeping (we took the stroller with us) before the end of the appetizer). The server offered to cut his meat for him!!! LOL.
I think travelling with an infant on the cruise can be a bit intimidating but it is a blast. This is why we are doing a second cruise. It was fun for the kids, and we got to be pampered and relaxed as well. They didn't have flounders then, and really no babysitting either. But we still had a fantastic time!!!