We did a 7 night cruise when DS was two, however as others have posted we stuck to our home schedule. One of chilled out in the room during nap times, and again at bed time - 7pm EST.
Our son had never been to daycare and was miserable at the nursery. We tried twice and both times got calls that he had not stopped crying after 20-30 minutes. We did not try again.
The splashpad was fine, but it was often crowded and no one enforces age limits. I took a full running elbow from a child much too old to be in a splash pad - would have knocked DS out cold had I not jumped in front of him. I ended up with a baseball sized BLACK bruise on my arm for two weeks. So be on guard there.
All of that said, we had a great family trip. It just wasn't action packed. He loved the characters, and the Disney jr activities. Our servers had watermelon waiting for DS every night when we arrived at dinner. We'be been one one more cruise with him since then (at 3 years old) and are booked on a third over NYE this year. All one week cruises.