All of the cruise lines offer Alaskan cruise tours - just that some are better than others. It really depends on which cruise line you like, where you want to go, and how long you want to go for.
Holland America does Alaska the best because they've been doing it longer than everyone else, has more cruise tours, and own all of their own lodges and hotels. Some of the others own their own lodge, but not their hotels. Some don't own anything.
Of course HAL is for an older demographics, yet they can still be good for children. But with that in mind, you might want to consider Princess. They would be my second choice for an Alaskan cruise tour because they are also very good and tend to cater to a younger crowd.
Royal Caribbean would be about 4th on my list. While they have a good children's program, they don't own any lodges in Denali, so if that's one of your destinations, you might want to look at other options.
Best advice is to work with a reputable cruise specialist who has firsthand knowledge of Alaskan cruise tours and let them help with all the many options you have available.