They did not charge us, but I did state that the rollaway was for a child. However, when we checked in I had asked about a fridge and when they told me it would be $10 per day (YIKES!) I did ask if they could waive the fee. She then said, "Well, we are already not charging you for the rollaway..."
So, I think there is a fee but I was never told of it and never charged it. On my reservation I believe it did say "rollaway-child" so perhaps that was the reason I was not charged.
I know if you call them directly you will get the answer, but if it is for your child I would make sure that you clarify the need for the rollaway when you ask.
BTW, we did not get the fridge! For $70 dollars I can haul a lot of ice to the cooler for the same purpose. I know we could have used the minibar fridge but it did not seem to get that cold and I needed to keep the baby's bottles very cold so I did not use the minibar. I asked them about it at the desk and I was told that the minibar fridges do not get that cold. Oh well, no big deal.
We had a great time and I know you will enjoy the Dolphin!