The Duck tour in Ketchikan was fun, even the adults. A bit silly but the younger kid can get a duck call and make all sorts of noise. It's a nice short tour of the town and water too.
Certainly get up to the Mendenhall Glacier and walk around. It's wonderful up there.
We loved the train although my young son who was 8 at the time did fall asleep at one point. IMO the views are much better than the drive on the road across the valley.
Here's a youtube video I posted. You won't want to watch all 10 minutes of it but glance through and you'll get an idea of the train ride. This was returning to the town from the pass and we were lucky and had a perfect morning so I was able to spend the whole trip between cars outside.
YouTube - ‪White Pass RR Skagway‬‏
You have to know your likes and dislikes when choosing your outings. Personally there are places and events I know I'd hate but I'll read how much others loved them. So think about that aspect of it.
I'm envious. Enjoy the trip.