The bigger ones may be more stable with less chance of sea sickness for kids. There is also a better chance of other kids on a bigger ship. Some companies have special family departures during summer months. Have a great trip.

We took our 6 year old grandson to Ecuador and the Galapagos Islands and it was an incredible experience for us. He loved it, we loved it and there are tons of wonderful memories. Here's a link to my journal and photos. http://www.janeandken.com/ECUADOR/Introduction.html You will see just how much fun a child can have--and grandma and grandpa.