We bought the Cosco Scenara car seat ($39 at Walmart) special to take lo to Playa Mia in Cozumel. The cab drivers were impatient and not thrilled, but install was quick and they drive crazy, so it was worth it to us, plus they charge full fare for her. The seat is super light and easy to carry around. The shuttle buses in Progresso didn't have seat belts to install it, but we had left the seat on the ship since we were just walking to the beach. The umbrella stroller was perfect for getting around the ports.
The long dinners were a bit of a struggle, but I packed activities for each night in a new backpack. The Pom poms from the dollar store in her snack trap were a hit one night, the iPhone games one night, stickers were especially popular, the dining room kid menu doubles as a coloring page and they have crayons, magna doodle was also good. The dining room is pretty loud and we were in a booth, so we didn't have to worry about her too much.
Camp Carnival starts at age 2, but she didn't want to be left alone there. The phone they give parents was handy to have since we traveled with the grandparents. They did allow her to come to the under 2 playtime where parents are required. On a particularly slow day they allowed me to come in and play to try to get her comfortable to stay. Overall, the staff was very kind and accommodating. The kids seemed to be having fun. The Triumph had a good toddler play area outside, but seas were rough and due to wind it was closed a few times.
The rough seas didn't bother her at all or any other kids I saw. The staff and crew all engaged her and genuinely seemed to enjoy having children around. We got an inside room, it was pretty small and I wish we would've got the ocean view room which was bigger and had a couch. She is in a toddler bed, so I requested the crib mattress and made up a bed on the floor. The upper bed seemed too dangerous. Sometimes in the afternoon on sea days, we were left looking for things to do, so we'd try to find an empty lounge and let her run around.
Overall, I'm glad we took her. We had fun, but I think she'll enjoy herself more when she can swim in the pool and feels comfortable being left at Camp Carnival. Having the grandparents along helped a lot, I recommend it if possible. I wish we would've had a loud fan to help block hallway noises, she woke early and only napped one day. I'd be glad to answer any questions.