do your kids get car sick when they travel with you? If they don't then you really don't have to worry about motion sickness on the ship. The ships have wonderful stabalizers.
I would pack the Bonine ( works better than Dramamine- imo), get some ginger snap type cookies just to be on the safe side. They will be so excited and so busy that they really won't have time to think about motion sickness. Keep them outside in the fresh air and if they start to feel the queezies, grab a glass of ginger ale, keep them busy,get something salty into their tummies also and if that doesn't work then take the Bonine.
IF you child gets motion sickness in the car or on the airplane then the wrist bands are a great idea. They work great. The patch is an absoulte last resort. I don't think they even prescribe them for children, they contain anti-seizure medication.