Welcome aboard, April!
You're going to love the Youth Clubs aboard the Dream. If you'd like to schedule time for your son to enjoy It's A Small World Nursery while you sneak off for some adult time, be sure to make advanced reservations, as those time slots do fill up. On embarkation day, there will be a few open hours where you can join your son in It's A Small World to help familiarize him with the surroundings, and play a bit together. Schedules are always subject to change, but I did notice before that there was at least one other time when parents could join the child in the nursery to play. However, the majority of nursery time is for child care while you're off exploring the ship's other activities for adults.
Another spot you might want to try is the Oceaneer's Club. You are welcome to take him into the Oceaneer's Club and Lab during one of their Open House times throughout your cruise. Typically the Oceaneer's Club and Lab are for ages three to 12-years old, and are great spaces for them to explore on their own with the counselors and characters who stop by, while their parents are enjoying the adults-only areas of the ship. However, during Open House times, all guests are invited to the Club to participate in the activities, parents staying with their children. Your son would find so many fun things to do. He'd probably love exploring Andy's Room with you, or running around Monster's Academy in the
Oceaneer's Club, both of which you can read about on the Disney Cruise Line website.
I hope you'll find the Youth Clubs on the Dream to be as much fun as our whole family does! Check out our Personal Navigator once you're onboard for specifics on Open House times, and have fun with your son!
Let me know if you have any further questions before you set sail, April!