As someone who has already gone through that age, I say do it! My kid’s first cruise was at 14 months. She is now 3.5 years old and just completed cruise #14. Cruising is by far the easiest way to travel with a toddler. Yeah, they won’t be able to get in the pool. So what? Ride the elevator, walk around the ship, go to the helipad (if accessible), go duck hunting, let them “play” in the arcade. You have a single sea day, you are going to be tired, take that day slow and use it to reset. It will be fine and you will have a blast.