If it were me, Mary Ann, I'd probably avoid the Magic Kingdom completely on Thanksgiving Day. You can count on Magic Kingdom being
the most crowded park that day. However, if you have your heart set on spending Thanksgiving there, you can opt for
Liberty Tree Tavern, which provides a traditional Thanksgiving meal every day of the year, or for
Tony's Town Square, which, historically, has offered a special Thanksgiving meal just for the holiday.
My personal recommendation would be to avoid the parks altogether on the holiday and spend the day, instead, enjoying a delicious meal in one of the signature dining locations. You might also choose to do some shopping at Downtown Disney, or visit the movies. Either would be a much more low-key way to spend the holiday and avoid the crowds in the parks. Good luck with your decision!