Scott Cawthon's hinting of paranormal activity within the pizzeria gave rise to speculation that the ghosts of the five children (and the other victims) might have possessed the animatronics, which caused their violent behavior.
Another theory speculates that the missing children were stuffed into the four animatronics. This would explain the animatronics' foul odor, the leaking blood and mucus, and the parents' comparisons to reanimated corpses. No one knows what happened to the fifth child, though it is believed that the fifth child may have been stuffed into Golden Freddy. This could explain why Golden Freddy has a little girl's laugh. However, It is possible that all of the children were killed and disposed of in a more traditional way, though.
In the Take The Cake to the Children Death Minigame in Five Nights at Freddy's 2, the murder of a single child is witnessed. This would indicate that the murderer has struck multiple times, and that there are a total of six known children killed. This is confirmed in the Happiest Day minigame in Five Nights at Freddy's 3, where the six masked children gather around the cake before disappearing.
