We're on the same cruise as you! No kids ourselves, but we went on some excursions where others had young children with them. I think they overestimated the young ones stamina and interest in the excursions. One was the round trip steam train excursion in Skagway - beautiful scenery but not much to hold kids attention - the ones in our car spent most of the time fussing and asking when it would be over. The other was the Neet's Bay Bear Watch by floatplane - the young kids were amazed at the bears for the first 10 minutes, but after that they got bored and tried to amuse themselves by running around and squealing - not very safe in that situation with the animals around!
Sorry I can't recommend any specific excursions for kids, but I'm sure others will chime in here. When looking at the
DCL website, each excursion will have the duration noted - many can be quite long and only you will know how much stamina you and your kid will have.
Maybe we'll see each other on the cruise!
Aby