Lisa Robin Kelly resumes the role of Laurie Forman after a two-year hiatus. Kelly left the show mid-way through the 3rd season, due to her alcoholism.
Even though it is insinuated by the characters that a kids' table and an adults' table at Thanksgiving dinner is an annual set-up, all previous Thanksgiving dinners at the Forman house were held in the dining room. Donna and her family (as well as other guests) would only come for pie afterward.