^^ What lbgraves said about taking Bonine starting the day before the cruise. One pill, once a day, until you are done with the cruise. If your "sea legs" come back on land with you, take the Bonine a few more days.
DO NOT use the patch without trying it first on land. It makes my whole family sick. I tried it last year before my cruise and it made the whole room tilt and I got dizzy; the same thing happened to my sister and my mom.
We all get very motion sick (trains, planes, automobiles, merry-go-rounds, you name it) so I was hesitant to cruise. LOVE IT!! Have I had some sea sickness over the years cruising? Sure, but not enough to keep me off of ships. You are going to feel motion at times but, as someone else mentioned, there is nothing like being rocked to sleep by the ocean. Unless I'm in pretty rough water, I'm okay. If I'm in rough water, even the Bonine doesn't help. I have to stay in bed until it's over.
I love to cruise and I'm even going to test my seasickness against a TransAtlantic cruise this fall. That's how much you are going to love to cruise. Just be prepared and don't worry about it. Also, take some hard ginger candy for your kids (or ginger tea), there's nothing like ginger for a sick tummy.