Hello, Yuki!
Welcome to planDisney. It's so wonderful to have you visit us as you prepare for a Disney Cruise! Your 9-year-old is going to have the best time ever onboard. There is
something for everyone to enjoy, and that goes beyond the entertainment and fun found in
Disney's Oceaneer Club.
If the nine-year-old in your party wants to stay in the room to rest, watch Disney movies on demand, and enjoy the stateroom amenities, they are welcome to do so without a parent in the room. In fact, once a child is 8 years old,
parents may grant "self-check" privileges to their children for Disney's Oceaneer Club. This means that the child may check themselves into or out of the kid's club as they'd like.
My kids loved the extra independence that they felt when I allowed them to check themselves into or out of the Oceaneer Club. In my experience, it is helpful to have a notepad in the stateroom to write messages to one another (especially if the children in your party don't have a smartphone). If my kids wanted to go back to the stateroom and they found I wasn't there, I'd leave them a note so they knew where to find me.
I hope you find this information to be helpful. Please sail back to planDisney if you have further questions. My pals and I are here for you!
Have an incredible sailing, and Happy New Year!
Adrianna