I just had a theory of FNAF 4 that I don’t think anyone else has brought up yet:

What if there’s a more specific reason as to why the little boy is scared of the robots and the restaurant as a whole? What if it involves the little sister of his that we don’t even see (but instead only see her empty room with just a mangle lying there)?

My theory is that possibly a year or so before, this little boy witnessed his little sister being lured away by someone in a Springtrap or a Golden Freddy suit (purple guy), but he’s just a child. This little boy didn’t know it was some serial killer, he probably thought that the robots hurt his sister—

And what if the little sister ended up as Mangle, or at the least, ended up the same way Mangle did: torn/hacked to pieces by the killer? Either the little sister was hacked to pieces/dismembered in order for the killer to hide her, or her soul ended up in the Mangle eventually (because Mangle is a character from the second pizzeria from FNAF 2, and she’s the only toy animatronic character we see in this fourth game as a phantom, aside from balloon boy).

(this is clearly a little girl’s room, but the question is why don’t we see her at all? well maybe we do, right there on the floor next to her bed)

So basically this little boy is beyond terrified because he thinks the robots take kids and kills them. He doesn’t know it’s some serial killer who preys on kids, because that was not what he saw. He saw someone dressed as an animatronic/in the suit to lure and “take away” his little sister. And the older brother probably got tired of hearing his little brother constantly bringing up their little sister being “taken away by the robots”, and for all we know he was supposed to be watching the little sister when she got taken away/lured, so any mention of his sister makes him angry and annoyed, hence why he ends up being /so/ cruel to his little brother as a result.

and not to mention what else the little boy saw:

which probably didnt even nearly affect him as much as it should have. when you’re a child your fears are amplified, especially in the form of nightmares. after seeing his little sister being lured away by supposedly (in his mind, again, as a scared child who wasn’t aware of what actually happened) either the Springtrap or Golden Freddy/Fredbear robot. So why else would it be ironic that the little boy who saw his little sister being lured away by a serial killer happens to stumble upon the actual killer helping someone/a worker in one of the many suits there? It would be a horrifying coincidence, but all those nightmares this little boy had, thinking the robots would get him the same way they got his sister… its why, in his mind, this purple man doesnt seem like a threat to him. Because he didn’t see the purple guy, he saw–

–one of these robots lure his sister away.