I was traveling with my husband, two kids (19 month old daughter and 3 yr old son), my sister, and her boyfriend. This review is pretty family-focused.
We arrived in Miami a day early and stayed at the Embassy Suites Miami Int'l. The hotel was fine, but not great. I used points, so I have no idea what it costs. Breakfast was quite crowded after 7:30am. My 3 yr-old loves airplanes so the view of the runway from our hotel (from the pool-view rooms) was a huge highlight for him. It was loud, but considering how close to the runway you are at the Embassy Suites, I was actually impressed with the level of noise control.
The day before the cruise we went to the Miami Children's Museum. I hadn't seen a lot of reviews on it, so I had some unanswered questions before we arrived. My husband's aunt and uncle met us there for some time with the kids. I wasn't sure ahead of time if there would be places for the aunt and uncle (in their 70s) to sit as we went from exhibit to exhibit (there were) and I didn't know if it would be as interesting and safe for my 19-month old and my 3 yr old alike (again, it was.) We spent a couple hours and could easily have spent more time there letting the kids play in their favorite areas (for my son it was the fishing area). I did know they had a Carnival Cruise ship mock up display, but was disappointed that it didn't have a whole lot for the kids to do in it. But the rest of the museum was such a hit that that wasn't much of a disappointment. The museum has a Subway restaurant which provided a good lunch for us. We sat outside and had a perfect view of all the the cruise ships. If you arrive in Miami early and you have kids, I highly recommend going to the Museum. Everyone over 1 yr - $10. Under 12 months - free.