With the recent U.S. vaccine approval for children aged 5 to 11, Disney Cruises has upped its passenger Covid requirements; as of January 13, eligible children will be required to be vaccinated before sailing, like their parents.
Most cruise lines already require vaccination for children 12 and older; Disney is the first but likely not the last to extend the rule to younger children. Children younger than 5 will still be aboard, but with testing and restrictions.
The testing for the younger children will be at family expense; Disney has a negotiated rate of $98.33 for a third-party vendor if parents haven't made their own arrangements. That's separate from the paid-by-Disney (or if you prefer to think of it that way, included-in-ticket-price) PCR test that all passengers must take at pierside before boarding, regardless of vaccination status.
Children's vaccination status also affects Disney shore excursions. Families with unvaccinated children can only go on Disney-supervised shore trips, while vaccinated families can choose between Disney tours and going on their own. The excursion rule won't apply to stops at Disney's private island, Castaway Cay.
Disney has notified affected families with upcoming cruises, and is allowing cancelation or modification through December 1.