Donna's suggestions are pretty good. After whale watching in Juneau, a stroll along the main street, with a stop at the Alaska Fudge Factory would probably make the litte one (and some of the big ones) pretty happy
Skagway offers an excursion where you go panning for golf, which they might enjoy as well.
Ketchikan - as Donna said, it's a cute town to wander around. You might want to look at a Salmon Bake there, or the tour to the Totem pole park.