Welcome aboard, Heather! You must be excited to plan your Disney Cruise Line vacation for early next year! The cruise is certainly the best part, but planning is half the fun too!
If you are sailing in the Bahamas and Caribbean, your children do not need passports, only their birth certificates, if they are under 16. You can read details about the
travel documents that are required on Disney Cruise Line's website.
However, I still recommend that all families travel with passports for each person including children. My kids have passports and we feel at peace knowing that even if some emergency should arise which causes us to miss the ship in a port, we would be able to more easily get home. During the cruise, we keep our passports locked in the safe in our stateroom. Then, we always take them with us when we head out to explore the ports. You just never know, and we like to play it safe.
You might consider looking into getting passports for your kids since you have time before you set sail next year, but if you decide against it, they children will certainly be allowed to sail with their birth certificates.
I hope that helps as you continue planning, Heather. Please let me know if you have further questions! I'm happy to help!