In Cozumel, we didn't do any excursions...we took a recommendation from a previous disney cruiser and headed to Mr. Sancho's. It is a beach/activity area with a wonderful restuarant and some small shops. The people are wonderful, the beach is beautiful, the food is outstanding. There are so many things to do there for people of all ages, and for the 14 year old, a water trampoline...very cool. Along with atv rentals, horseback riding...there is also the most beautiful large hot tub. Wonderfully clean bathrooms/shower areas. Locker areas. We had a blast there..would love to go back again. We took a taxi...it was $15 for both of us..I hear it is that for up to around 4 people..but, you would have to negotiate that with the driver, on the sign it said Mr. Sancho's $15, so it probably would have been that for a full cab. They use mini vans..so your whole family would fit in. You can check it out at mrsanchos.com.
In Grand Cayman everyone raves about Stingray City...we did not try this, as it was our first time to the island and we wanted to explore. So, we got of the ship..headed to the taxi dispatcher and took the two hour cab tour. It took us to hell, the turtle farm, drove us around some of the nicer neighborhoods and then he would drop us at the beach if we wanted. I can highly recommend the turtle farm...it is so much fun. You get to hold live sea turtles..be sure to take your camera. Hell is ok...the best part is mailing your postcard from hell's post office. Then when the tour is over..the driver drops you right back downtown for shopping. Well worth the $15 per person. I don't know if kids are cheaper. We did a little shopping and then decided we would rather visit with the locals..so we went to two of the brewpubs/restaurants. Rackham's...a little way down on the left from the dock...oceanside, the deck overlooks the ocean, the food looks and smells wonderful, and for the beer lovers in your group the stinray city light and dark beers are both wonderful. They also have a great souvenier shop...in fact that is where we got all our soveniers for everyone...better prices than most the other shops in Grand Cayman.
Then we walked back towards the port and stopped at Big Bamboo...also wonderful. They grill fresh food for you on their deck, also overlooking the ocean. They have 5 microbrews there, made onsite. The staff is wonderful. The food was delicious...however if you are looking for a bigger, fuller meal..eat at Rackhams...we will definately eat there next time. We tried the food at Big Bamboo this past cruise.
In Key West, we had been there before, so we tried all the places we didn't try before. There is a great turtle museum down by turtle krawl. Also...for an excellent lunch...go to Bo's fishmarket...yummy, yummy and very reasonable cost. The sandwiches are so large, hubby and I shared one with a side of 6 conch fritters. The trolley tour is wonderful, it gives you a great overview of key west. Also...renting a golf cart (those new kind that look like space cars) is excellent...you can get two or four seaters and it is a great way to get around key west...the people who rent them are excellent..we orginally got ours for 4 hours...by the time we had driven everywhere, eaten, it was less than two hours...so we decided to make a couple more stops and return it at the two hour mark. We didnt even have to ask for them to credit us for the two hour time..they just said, we won't charge you for the last two hours, he changed everything on the paperwork and we were off to do the things within walking distance.
Have fun!