“Barbie” may soon be joined by another Mattel doll on the big screen. The toy company announced Wednesday that it's developing a live-action film based on its American Girl doll line. The project adds to the already teeming pipeline of movies in development for Mattel Films. Following its blockbuster first release, “Barbie,” Mattel Films is prepping live-action movies based on Hot Wheels, Magic 8 Ball, Polly Pocket, Rock ’Em Sock ’Em Robots and UNO. “Saturday Night Live” has already spoofed the idea of an American Girl doll movie. In April, it aired a parody trailer in which a handful of American Girl dolls from disparate eras of history are brought into modern day but keep dying of cholera.