We just got back from a cruise with my 3 and 7 year old. I was very paranoid before we left about the sea sickness and the flight. I wasn't sure how my 3 year old daughter was going to handle either one. She gets car sick on occasion. I bought Dramamine after consulting with her doctor before we left. They recommended giving it to her 1 hour before the ship sets sail. She didn't even need it. She was sleeping when the ship left port and it never bothered her at all! It's better safe to have it along, but I would say give it to her before you set sail if she'll take it (dosage is on the box) and then I wouldn't worry about it after that unless she says she can feel the boat. It's a mind set. If you don't make a big deal out of it I don't think they even know. And like I said. Give it to her before departure and tell her this will keep her from getting sick the whole trip and she will mentally set herself. Hope it helps!