We were very impressed with Carnival. We didn't have high expectations going into it, concerned about having a small child on a boat. But it was a large family trip and this was the time that worked best for everyone, so we packed our bags and crossed our fingers.
The staff were GREAT with our 17 month old son. He got lots of attention, the food was delicious and had lots of options for him. We ate dinner every night in the Golden Pearl, and the kid's menu choices were nice although leaned on the unhealthy side (cheeseburger, nuggets, pizza). However, there was always a pasta option, and it came before the adult's dinner and was a bit cooler so he could start eating sooner and we could enjoy visiting in peace.
I would definitely bring a child this age on this type of cruise again. Just a few things you might want to know though: I was unable to find homogenized milk anywhere, so he had 2% all week. We just grabbed containers at breakfast every day and had bottles in our room that we would wash out with a bottle brush in our bathroom sink. Our son luckily doesn't care if his milk is warm, not sure what you'd do in that case. And at his age, he can get away with a little less fat for just a week. But if you had a 12 month old, you might want to bring formula to ensure baby is getting all the nutrients needed.
Restaurants had no disposable bibs or wet cloths, but when we ate in the lido, we'd just grab an extra utensil set and use that napkin dipped in hot water from the tea / coffee area to clean him up. At dinner I just used wet wipes.
There were no garbage bags in the can in our room, so we ended up keeping the can inside the shower, both because of the smell and because our son would definitely play with the garbage if it was out in the room. Bags would be good to pack for this reason. Luckily, the room was cleaned twice daily so the diapers never sat for long.
We chose a balcony room so we'd have somewhere to hang out while our son fell asleep. It was a great choice for us. We got to feel like we were still enjoying the cruise instead of just sitting in our room quietly waiting for him to fall asleep. My husband rigged up a sheet between the crib and our bed using rope, sticky hooks, carabiners and clothespins because if our son wakes up and sees us, he figures it's party time. If your kid is the same, I would HIGHLY recommend bringing supplies to come up with a similar barricade. There is babysitting service on board, but our son is not good with strangers so that wasn't an option for us.
A couple big downsides: the Camp Carnival is not available for under two year olds. However, on sea days we were able to take him in there and play with all the toys. It was definitely one of his highlights. Another was that U.S. law doesn't allow kids in diapers into the pools or the water park. So if you don't have a potty trained kid, you're stuck on the sidelines. We did however notice there wasn't really any monitoring of this, and I'm sure if you wanted you could probably just bring your child into the pool until told otherwise. I mean, those swim diapers hold in the gross stuff, and we all know every kid under 5 years old pees in the pool anyway : )
The crib was small-ish, but good for our son's size. And it was good for the room size so we weren't overcrowded. We packed a playpen sheet but didn't need it as they put a large sheet in there folded over and even though he moves a lot, it never came out.
We brought a power cord as the one plug-in didn't cut it for our sound machine / nightlight / power cord for charging stuff.
We took a couple formal family pix and with our large extended family, the process was still quick and the pictures turned our great. This is an easy way to get everyone looking nice in one shot.
Anyway, I think that's about all that was relevant to travelling with an under-two year old. Like I say, a few things to make note of, but overall a great experience and one I'd do again. Our son loved the cruise, loved splashing on the edge of the pool, watching the people and water, toddling around the lido deck and hanging out on our balcony. Fun times for sure.