What ships offer child care for 6 month olds
It is easier to give you the list of ships which do not have a nursery, then those that do. At the time I am writing this the ships in the fleet that DO NOT have a nursery are Empress, Majesty, Jewel, Adventure,Explorer and Voyager of the Seas. Other than that you are covered.
If your are looking for ships that also have a baby splash area for children in diapers, that will narrow your choices down to ships in the the Freedom, Quantum and Oasis class. Just something to keep in mind if that is important to you as well.