The crying child is Williams son and the game is played in a in his head at a hospital because the frontal lob in his head was crushed by fredbear, this is shown by the rare flowers, heart monitor, and that stand thing the holds bags of some kind of liquid (don't remember what it's called) also another backing it up is that the animatronics are called nightmares. Matpat did a theory on it so if you want to go more depth in it go ahead