William Afton's daughter, at least in the games, is Elizabeth Afton, whose spirit resides within Circus Baby. While she was once a loving and energetic girl, her death at the hands of Circus Baby turns her, like the lost children before her, into something much more malicious. Eventually,...
Don't associate William with that character from FnaF because that's rude and I believe there are several characters with that name, imagine a William hearing you make jokes about Afton and calling them "purple guy" or something? I'd be really annoyed....