Welcome aboard, Catherine! I'm excited to hear that you're planning a multi-generational family cruise with Disney! My family has sailed as just the four of us but we've also included the grandparents and the kids' uncle in a few cruises too, which has made for even more wonderful experiences! You're in for such a great time!
I'm happy to let you know that the Youth Clubs, including the nursery are always happy to include children with special needs. The counselors have lots of experience with all different types of needs and are so wonderful about making sure those kids have just as much fun as everyone else in the clubs. Since your grandson is three, he's at the perfect age to enjoy some time in the nursery when the grownups sneak away for adult time. Just be sure to pre-book a few times for him there as hours do fill up. You can do this 75 days prior to sailing when you begin online check-in. You're welcome to add additional nursery time or switch your pre-booked time onboard if availability is there. Just be sure to check the cancelation information on the
It's A Small World Nursery webpage so you're prepared.
Then, I'd suggest that your family swing by the nursery during Open House hours on the first day of the cruise. Your son and daughter can hang out with your grandson in the nursery to introduce him to the area and get him acclimated, as well as chat with the counselors there about your grandson's needs. The counselors can help with any specific questions they have.
I hope those details help as you continue planning this exciting trip, Catherine! Please feel free to stop back again if you have other questions about cruising with Disney! I'm happy to help!