On our first
DCl cruise our daughter was 10 months old. She has been on all the cruises below, so we have probably experienced about everything possible with a toddler on the ship.
I think the most difficult part for you will be dinner. Be sure to do early seating. We also ordered her food first so she could eat, and then if she was restless by the end, she could go to Flounders.
We used Flounders quite a bit during the evenings. For the most part our DD was happy to play after dinner and then go to sleep. We would always check in to make sure she was sleeping at a reasonable hour. If not we would pull her out and take her back to the room.
My biggest advice is being able to go with the flow. Sometimes they cooperate and you can see the whole show, and sometimes they don't. If I could figure out how to get a 20 month old to cooperate at all times I could make enough money to live in the Walt suite year round (which is my ultimate dream by the way).
On our last cruise she graduated to Oceaneers Club. She turned 3 on the cruise, so she was the youngest in the club. But she is also the youngest in her preschool class so she is used to playing with older kids. She had a ball, but there was no way she would go to sleep in the club (some kids did as they get mats out, turn down the lights and put movies on). So our nights were a bit earlier, but a nice benefit was I was up earlier and saw many sunrises at sea.
Also, if they are still in diapers, you can request a diaper genie.
Good luck.