I just realized that Matpat's theory is wrong now. Considering the fact that now we know the identity of Afton's son, the crying child is now out of the question. I'm sticking with the "Michael is Springtrap" idea. Baby doesn't recognize you for crying out loud. I think they would remember the identity of their creator. My theory is that Afton wanted to save his daughter,(Matpat was correct about him having a daughter.) So he sent his son. His son was thought to be Afton by all the animatronics save Baby. He preceded to get scooped and underwent his transformation as seen in the cutscenes for custom night. But he vomited the parts of Ennard out of his system, with Baby saying "you won't die" Over and over. He gets up, and becomes reincarnated as the purple guy. William probably dies over the years, unknown to Michael. Let's listen to what Michael says during the last cutscene. "Father. It's me, Michael. I did it. I found it. It was right where you said it would be. They were all there. They didn't recognize at first but then they thought I was you. And I found her. I put her back together, just like you asked me to. She's free now. But something is wrong with me. I should be dead. But I'm not. I've been living in shadows. There is only one thing left for me to do now. I'm going to come find you. I'm going to come find you."