We went on an Alaskan cruise a few years ago when our daughters were 10 and 4. Our ports of call were also Ketchikan, Juneau and Skagway. In Ketchikan we hiked around on our own and went to the Lumberjack show. In Juneau we went on an excursion that included a whale watching cruise and a stop at the Mendenhall Glacier. In Skagway we went on an excursion that was a bus trip into the Yukon and the White Pass Railway back to Skagway. The highlight was definitely the dog sled/kart ride that we did when we stopped in the Yukon - anything to do with sled dogs was a hit on the entire vacation. The train ride was fun - my younger daughter did get tired of just looking out the window but we had stickers and books with us to keep her occupied while everyone else enjoyed the ride.
I have a trip report and photos on my travel blog at Gone with the Family
if you would like more information.