Hi William,
Good news! You will easily be able to pop over to the Grand Floridian for your dinner at
Grand Floridian Cafe, then return for an evening at
Magic Kingdom. No car necessary.
You have two transportation options from Magic Kingdom. You can catch a boat from a dock just outside the Magic Kingdom exit. Look for the one marked
Grand Floridian. Or you can hop on the resort monorail. It will circle Seven Seas Lagoon, stopping at the Contemporary, the Transportation and Ticket Center and the
Polynesian Village Resort enroute to the the Grand Floridian.
Either option will take 30 minutes or so. The boat can sometimes be faster, as long as you don't need to wait long for it to depart.
To return to Magic Kingdom, I'd recommend the monorail because Magic Kingdom is the next stop from the Grand Floridian. The ride is less than 5 minutes.
Thanks for dropping by the Disney Parks Moms Panel, William. Please let us know if we can answer any other questions for you as you plan your visit. Enjoy!
Wilma