I would also check / follow up with guest services the day you sail. Our last cruise we were put on late dinner. (which everyone* had agreed to). My DS was a toddler who never liked to sit still in general, so for a while eating out was a NO GO. We used the nursery services and loved it. Yes, it is extra money to pay, but having a nice dinner was great, and our hosts were amazing and gave us food to take to him for later. (Usually we made sure he ate BEFORE the nursery, because he was usually down asleep when we picked him up.)
On the switching side of things, after our first / second night onboard, my father* admitted to hating having to wait to eat so late, and wanted it changed to the earlier option. Since he was paying for the cruise, I went to guest relations to see if anything could be done. (By the way, the guest relations people were amazing, patient, and kind. Suffice to say, it wasn't the first or last time I had to speak with them due to family drama on that cruise. -_-;; )
We were switched, but it caused a BIT (LOT) of confusion as we were also assigned two new waiter staff even though our waiters were still working the early rotation too. My husband and I felt horrible, and we assured them that the change wasn't because of anything they had done - We loved them so!. -_-;; (Also at the end we had four wait staff tips instead of two - They ALL were excellent.) This was when the Fantasy was extremely new (Maiden voyage was previous sailing or so), so it's possible by now they have this scenerio figured out.
Personally speaking, I LIKED the later option. I always felt tired after dinner, and opted out of a few shows because of it. (Although the idea of kids watching the show in their pjs is appealing!) The later dinner meant taking in the show first, then dinner, and then no guilty feelings if I got tired about 'missing' stuff. Our next cruise we decided to go late again! (Although this time just our family and my DS WILL be joining us.

lol )
But planning ahead if at all possible is ALWAYS better! I wish you the best of luck and hope you have a great cruise OP!