As Tom is one of the very best advisors in the cruise industry, I agree that RCCl is an excellent choice for an Alaskan cruise for your family.
Some additional ideas...a RT cruise from Seattle might be a little easier on the kids and your parents, that is, not having to go through customs and the airfare/driving might be less hassle.
Consider renting a car in Juneau and Skagway as this should give you more flexibility and cost savings over tours.
Re the kids...get them involved with the planning of the cruise and make sure that they know it is an adventure and not just another vacation.
Hope that you have a great cruise.