William Afton’s reasons for killing children are never explained in a single clear line in the official Five Nights at Freddy’s canon, but several motives are strongly implied and expanded on in different media. Overall, he is portrayed as a serial killer with a twisted obsession, not someone with a sympathetic or justified reason.
Game and book canon
In the games, Afton is shown targeting children around Freddy’s locations, luring them away using a mascot suit and hiding their bodies in animatronics, which suggests he specifically preys on children because they are easy to trick and tied to the pizzerias he is obsessed with. In the novel trilogy, his backstory hints at an empty, unpleasant past and a disturbed personality, and he kills because he enjoys it and feels powerful, which lines up with how a fictional serial killer would behave rather than someone with a rational motive.
Theories about his motive
Fans often point to jealousy and personal tragedy as partial explanations, such as jealousy of his business partner Henry’s happier family and the deaths of Afton’s own children driving him deeper into madness and experiments with animatronics and “remnant.” However, these details and timelines vary between games, books, and fan theories, and there is no single officially confirmed reason that fully explains “why” beyond him being a murderous, deeply broken person in the story’s universe.
