Notes

Some of the children's names are: Gabriel (Freddy), Jeremy (Bonnie), Susie (Chica), Fritz (Foxy) and Cassidy (Possibly Golden Freddy)
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.
In the Take 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 is 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.
It is confirmed, however that the killer was the Purple Guy (Real name William Afton) from the Death Minigames. Upon the completion of the fifth night of Five Nights at Freddy's 3, the player plays as the soul of a dead child, confronting Afton in a room with the four other dead children watching. Purple Guy attempts to hide inside Springtrap, but once in the suit he misuses it. This causes the locks that held back the animatronic parts to break, causing the springs and other various parts inside the suit to pierce into Purple Guy's body and cause him to die.
Okay okay, 1. William Afton died while being chased by kids' souls, which resulted in him being spring locked. 2. Mike is Terrence, Mike went back to being called Mike after Chris's death. (Sorry if that made no sense). Elizabeth/Liz, did not die from C.B. Liz died from being scooped. All C.B. did was store Liz in her storage tank, William Afton later decided to scoop C.B. for repairs and the scooper crushed Liz in the process. Clara did die in a car crash, and Ennard and C.B scooped Mike.
Ennard and C.B. (Liz) planned scooping Mike to use his body as a skin suit to be able to leave the pizzeria. And Ennard is a female because he is made out of scooped parts (60% of him is female) and C.B. is a part of him, which is why his voice sounds like C.B.'s voice. A lot of people reference Mike as Terrance because Mike stopped being called Terrance (The nickname Liz and Chris gave him) Chris's death because of guilt. (Mike's full name is Micheal Terrance Afton)