Okay so my party is currently traveling to The North to locate a school run by Cultist of Orcus; that are kidnapping/convincing parents of their legitimacy to slowly indoctrinate these kids into the cult. 

They have made it to the city you can go through Fool's March before you are in The North proper. 

The reason they are there is because a person from the Barbarian/Druid's backstory is being imprisoned for murder (she didn't do it). 

Another plot thread is going to be that a creature that is bound to the the location is attacking/ransacking people's homes or farms.

I'm not sure what kind of creature I'm thinking of. But I'm thinking something intelligent can't leave the surrounding area maybe a curse idk. Reason for attacking these places is they are convinced someone in Fool's March has taken their adopted child/ren (like I'm imagining they were abandoned and this creature has cared for them.) Because people there didn't think this creature should be caring for children. 

I'm thinking someone that most people wouldn't normally suspect would care about adopting children. I am playing loosey goosey with some creatures lore.

You could maybe have some kind of massive were-tiger that is actually a Rakshasa in its shapeshifted form. It could have been bound as a guardian for some kind of portal to other planes nearby due to an evil act commited decades earlier. It could then have become particularly lonely and adopted an abandoned human child and raised it as there own, the child never aware that its parent was actually a duplicitous shapeshifter. One day the child could have been found wandering the woods by some local hunter and when the kid couldn't answer where he was from, the kindly hunter brought them back to the village.

The temple to Orcus isn't kidnapping anybody. They're just getting a bad rap. The party can investigate and find nothing, no kids, no evidence.

The threat in inside the village where they awakened a hive temple to Tithonus (god of insects) while digging a new well.  Swarms of roaches have been making away  with the children at night. They are the perfect food for egg implants.

I assume that the children the creature was raising have actually been kidnapped by the Cult of Orcus? In any case, if you want it to be unexpected, that leaves a pretty wide range of creatures that potentially could decide to raise children. For things that have some actual mythological justification beyond "seems interesting", hags are oddly dual natured about children; sometimes they protect them, sometimes they eat them.

Whats the party level? I hear "children being kidnapped/going missing" and my head goes STRAIGHT to Oni! You can't go wrong with an appropriately levelled party with the horror/suspense ride that a well played Oni creates!

My party is at lv 8. And I do have a thing in my campaign about the origin of Hags. Could she have been bound to a specific location that prevents her from leaving the area?

Quote from sailorroxy >>

My party is at lv 8. And I do have a thing in my campaign about the origin of Hags. Could she have been bound to a specific location that prevents her from leaving the area?

 Well, yes! Its your campaign! Absolutely!