As the parent of a 2 and a 4 year old, I have to agree with the others. We leave our children at home because we feel cruising is our 'adult only' vacation.
That being said, I too, want to take our kids to Alaska one day; however, I feel they need to be old enough to KNOW what is expected of them in terms of behavior, etc. A 4 year old, much less a 2 year old, does not and for that reason we chose not to take them.
There is plenty of time for them to cruise, and they will, once they understand proper etiquette for doing so.
Just my 2 cents...
Anthony