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All of the major cruise lines have wedding packages. It really depends on how much you are willing to spend and what you want out of the cruise. There are many options. Doing the wedding package on one of Royal Caribbean's Freedom-class ships would offer a lot of things for the kids to do. They also have nice wedding chapels on those ships. With 6 people you have to look at cabins too. You'd need either two standard cabins or one of the larger (and expensive) suites or family cabins. Ships don't have many family cabins, and they book up quickly. This is true for all the cruise lines.
This is something that you definitely don't need to arrange by yourself by a direct booking or by using an internet cruise agency. You need to use an agent. The staff here endorses people using agents with CLIA credentials. You can find a list of CLIA-member agents near you by going here
and typing your zip code in the bottom right corner.