Would you be willing to book an inside or ocean-view cabin?
I have found when compared to other cruise lines the balcony cabins on DCL are way more expensive. When I booked ,with the 10% OBB discount an inside room is less expensive than other cruise lines (with the exception of Carnival).
Sure I would love a balcony but the difference is $2000 which I cannot justify.
ITA. We did Alaska this past June as well and had an ocean-view cabin. Although the weather was AMAZING (sunny and warm), I'm not sure we would have used the balcony if we had had one. There's just too many things to do outside the room.
As for in port, we planned our own excursions. In Skagway, the National Park Service hosts a number of activities and tours throughout the day. It's first come, first serve so get there early. You can also have the kids participate in the Junior Ranger Program. Here's a link to the park service website.
http://www.nps.gov/klgo/planyourvisit/index.htm Depending on how active your family is, you could hike some of local trails too. We hiked up to Lower Dewey Lake. The trail up to the lake is steep but once you get to the top there is an easy trial that goes around 2/3 of the lake. The remaining path is a bit challenging and may be too difficult for young ones. Don't forget to take bug repellent if you hike. The mosquitoes are vicious.
In Juneau, we did our own trip to Mendenhall Glacier (also part of Jr. Ranger Program) and spent most of the day exploring and walking to the base of the falls. It was nice being on our own because we could take as long as we wanted, unlike a number of families we saw running back to the visitors center to catch tour buses.
In Ketchikan, we visited the Totem Heritage Center (accessible via free city bus) and the Lumberjack Show. The center was very interesting but might not hold little one's attentions. The Lumberjack Show is perfect for families and within walking distance of the port. If you're going in late summer consider visiting the Fish Ladder to see the salmon run. Although we didn't go there, the Discovery Center participates in the Jr. Ranger Program too.
As for getting to Vancouver, it was much cheaper to fly into Seattle and take a train/bus to Vancouver. With little ones, I recommend taking the train. We went by bus and the trip took forever. Our coach made multiple stops on the way up and we had to get off the bus, with all of our luggage, at the boarder for customs. The return trip was faster with only a stop at the boarder. Even with hotel stays (hot deals from Hotwire) on either end of the cruise, coming and going from Seattle was cheaper.
All in all though, it was well worth the expense.
As another poster mentioned, the Alaskan sailings for 2014 have been available to book since Feb 2013. We originally booked the 6/16/14 sailing on opening day, then several weeks later we switched it to 6/17/2013 (up a year) so we could sail sooner due to a family member that was ill and I was afraid of the long term prognosis. I switched because the prices had not changed which was a little surprising - lol. However, I can see the 2014 sailings have gone up and some there is a chunk of change there (I use cruisefish to see the historical pricing). Our 6/16/14 sailing was not one of the "higher" peak season ones but for the three of us it's gone up $600 in a Cat 7A. For the Cat 9A it's gone up $1008 for the three of us - that's a big swing. I don't think you'll regret the decision one bit and several of us are waiting with baited breath on the 2015 sail dates so we can go again. Alaska was the best cruise and vacation we've taken and you'll absolutely love it with DCL!! 
As Linda said you can definitely switch up some of the excursions and thoroughly enjoy yourself. We spent about $730ish on our excursions for the three of us and in no way did we feel we didn't see or experience Alaska and we did something in every port. The next time we'll do different excursions to mix it up some.
