A.K.
I am a travel agent and I arranged an Alaskan cruise for my girlfriend and her family. She just came back and her 4 year old daughter did so well. She did not even needed to take any anti-seesick medicine (but bring it anyway) even though there were nights that were choppy. Her daughter had so much fun because it was something new and she was so distracted. As for dinner time, I highly recommend bringing a portable DVD player so the adults can enjoy a long meal. Please make sure to take the Glacier excursion...it is a must see. Also, make sure to bring a medicine bag for your daughter because if you need to see the doctor on board for any reason, it will be quite expensive.
Have lots of fun! Alaska is amazing. I was just there last Aug.
BTW, the next time you book a trip, visit my site, www.TravelWithKwan.com and book with me. :) The prices are really competitive to Expedia and Travelocity.
A.