Children tend to be much more tolerant regarding motion. We have taken our DS when he was 12 weeks at the beginning of this month. We have taken DD at 5mo, all the way up to 3yo on 9 cruises. No problems even when we have been on rocky cruises the adults had problems handling, one was even too much for us to go to CC. If you are concerned people often bring ginger type candies for adults and kids, obviously this would not be recommend for a bottle fed infant but there are gripe waters that have a ginger component. I don't have any advice for you on actual medications as luckily we haven't had to use any of these.
