hi!  Some  dear friends of ours from Australia took their young daughter (SWCAH) on a 14 day cruise.  They took all the necessary precautions like you but also spoke with the customer rep from the cruise line and was assured that one of the cruise ships had a helipad to allow for a helicopter to land and the other while it didn’t have a helipad they had arrangements with a company (like the convalescent transports that we have) that could make a water landing if necessary to take the child out.  Maybe you could speak with someone and just amke sure of what their procedure is.  I’m sure you’ll have no problems but just to set your mind at ease!!