I don't know if I will add anything or not. We are taking our first cruise this year as a family also. I have been on many cruises as a single adult but this is the first with kids. We looked into several ships in trying to determine if they had good kids programs. We chose RCCL for this reason. We also wanted to experience the beauty of Alaska as a family. Because there are excellent kids programs aboard, you may be able to book excursions as a couple only or book those that have families in mind. We chose whale watching and dog sledding for family trips and helicopter tours for couple trips. You can get kids discounts on several of the tours. We got both for whale watching and dog sledding. You can find many discounts from that offered by cruise if you book independently. If you plan ahead, pick wisely, you can find a common ground on what to do. Unfortunately, your 4 yr old will probably not remember much of it. It will be up to you to document it with video for he or she to see later in their life. If you had babysitting at home while you were away on the cruise, I am sure that you would have more fun. The family cruise will be special also, you will just have to work harder at it.
My now 15 year old started going to Alaska with me when he was 8, the youngest I would consider. Most kids have no interest in scenery or the long extended times Alaska travel demands for "action". Shore touring in this area is probably the most costly of any cruiseing area and certainally far more than the plentiful under $50 tours of the Caribbean. I would say if you can afford it- go. But it is an adult trip in my opinion. Kids programs are on all ships and would be enjoyable for most any child. Far more inportant in your ship choice is - COST, ports, time in ports- (longer is better), route- (avoid more "outside" sailing ships), glacier with Glacier Bay my clear preference.
I appreciate your input. The more and more I look at shore excursions, the less and less it seems like my boys will be able to do. To make matters worse, they would be in separate "camp" groups on many lines because of their ages.
Another posiibility I am considering is taking my nephews. They are 17 and 13. It will be the 17 y/o last summer before going away to college. This may be my last chance to have a fun adventure with them. Since my boys are so young (4 & 5), I used to travel with my nephews - a lot! Dude ranches, amusemant parks, skiing, etc.