You have 5 locks because of two reasons.
Firstly, and obviously, because of the demon children.
"Wow, you really LOVE them don't you?" A mocking voice comes from behind you.
Yeah, the locks neither work against the children nor HIM.
Nightmare the king of darkness or something like that.
You sometimes wonder if he is the one helping children getting inside. Well, they mostly leave cookies but that is like a bribe to silence you so you won't tell their parents.
You were definitely not a normal person.
Why you may ask?
First, you woke up in a weird place and touched some strange and obviously not a 'suspicious' mirror.
Then, of course, it sucked you into it.
On top of that, you got your body stolen and blackmailed to help a demon child.
You think you are a normal person, you have a normal job and an okay house.
Well, at least you thought you were a normal person until one day a barrier broke and frickin monsters come from the underground. Well, this wasn't NORMAL but not bad either (for you at least).
You may be asking how monsters coming from the underground affected you?
Because you were sure the reason you are haunted by a genocidal ghost child is their fault.