They can fill up. Usually at dinner time or late evening when adults want to go to the clubs.
But people do cancel too, and sometime syou can pick up a couple extra hours if you keep checking back.
Yes they change diapers. It is a minimum 2 hour stay, so they really need to do that

actually unless they smell something i believe it is every 20 minutes they do diaper checks, something like that.
Its been 3 years since we had a young grandkid with us.
But yes do book as soon as you can for the nursery.
You can always change once on board if needed.
sometimes on line it lay say its filled for the nursery or Palos.
Dont panic! They only allow a certain amount of hours to be booked on line. You can go o the nursery and book as soon as soon as they open that first afternoon, shortly after boarding.
They save lots of hours just for that.
Kathleen