When I was researching Volvo before placing my order, I found reference to both 3 and 6 month SiriusXM complimentary periods, e.g. https://volvo.custhelp.com/app/answers/detail/a_id/9047 and https://volvo.custhelp.com/app/answers/detail/a_id/9010/. I've tried it a couple times over the years, but like you, didn't use it or found too many spots I frequented where the signal faded, and I cancelled after a short while on subscription. I doubt I even turn it on when my new XC60 arrives, so I can avoid their customer service and repeated email/mail notices that never seem to go away.
...but more importantly for your children who like the service, I've seen reference in the past from an owner or two where the complimentary period didn't seem to ever end for them, and we don't know why. They also (purposely) never tried to send a refresh signal to their vehicle, or call/contact SiriusXM to ask or change their subscription level or profile (HINT-HINT). Enjoy while you are!