I've mentioned I'm a believer in Crying Child being Cassidy before, but never really elaborated on that, so I'll do it here with a theory I've been thinking about for a while, under the cut.
The Faded text and Altered text (who is definitely Crying Child) in the Security Logbook both claim to be Cassidy (Faded through labeling the clues as "My Name", and Altered through many repeated instances of "It's Me" around the name in the word search). Not only that, but we get the name Cassidy through both texts as well (with a little help from Mike and his red pen). Faded provides where to find the clues, and Altered provides the actual clues.
Faded text places the various instances of "My Name" seemingly in response to Altered asking in the word search "Who are you? What is your name?" But if Altered text provides the clues to solve the name, why would he be asking for the name?
Let's go back to the older entries for a bit. At the end of the game, Crying Child is told "You're broken. I will put you back together." The only time we see this phrase in relation to an Afton child is in the very next mainline game, Sister Location, where Michael says he put Elizabeth back together. If we look at Baby's dialogue in the game, we can see she goes from not even being able to recognize her older brother to recognizing him enough to mistake him for their father, implying she's recovering her memories. Which in turn implies that what is meant by Crying Child needing to be put back together is that he is missing his memories.
The game between these two, FNaF World, shows a figure represented by a pixelated Fredbear tasking you with finding clocks, which upon interacting with brings you to various mini games, where you set up the clues in FNaF 3 needed for the secret mini games there to get Happiest Day. And the Stitchwraith stingers in Fazbear's Frights directly tie Happiest Day to the alteration of memories.
Golden Freddy seems awfully aware of things throughout the series, even going back as far as the first game, in which he taunts Michael with those infamous "It's Me" messages before attacking him. But in spite of this, Crying Child still doesn't quite remember anything. Clearly, some part of him does remember, but he can't access it.
"The pieces are in place for you. All you need to do is find them."
Which brings us back to the Logbook. Where Altered text, Crying Child, asks Faded text for a name. Which is responded with places to find clues, clues that CC himself provides, with some help from Michael. And when those clues are finally put together to reveal the name Cassidy, we see a lot more "It's Me" around the letters.
I think the Logbook is trying to show us Crying Child finally managing to put himself back together and remember his own name. The name Cassidy Afton.
TL;DR, Faded and Altered text are both different "pieces" of Crying Child that need to be put back together through recovery of his memories, and upon achieving this goal, he remembers that his name is Cassidy.
