"Scooby-Doo" stars Sarah Michelle Gellar, Freddie Prinze Jr., Matthew Lillard and Linda Cardellini will hardly be able to catch their breaths before they hop on the Mystery Machine into a sequel to last weekend's No. 1 box-office attraction, reports Variety. The trade paper says Warner Bros. has set an accelerated schedule for Part II, which, like the original, is to be directed by Raja Gosnell. (Warner Bros., like PEOPLE, is part of AOL Time Warner.) Production is due to start early next year, for a summer 2004 release. Lorenzo di Bonaventura, the studio's president of worldwide productions, told Variety, "We're certain we've got another great Scooby-Doo story to tell in movie theaters two years from now." The first film took in a breathtaking $54 million in its first three days. Meanwhile more good news for the movie's Lillard, 32, who plays the ditzy Shaggy in the family film: He's a dad, for real. Last Thursday -- the day before "Scooby-Doo" opened -- his wife of one year, Heather, gave birth to a baby girl, named Addison Grace Lillard. The new arrival weighed 6 lbs., 10 oz., reports the Associated Press.