I think they're related, but unique creatures. Haunts whittle down children by presenting them with their fears to take possession of them. A Baku-Baku feeds off of fears of children (and adults) by causing them nightmares. They're both phobophages, but their modus operandis seem different. Haunts also seem to be a new type of creature that exclusively feed on children and can be seen by them (as hinted by Jim several times before when he's spoken about a potential young adult series).

I don't think they are new at all, I think they use whoever, in this case children to taken down their victim.   Harry didn't see them not because he is an adult, though both Maggie seems to think this is why, but because he has full control over his wizard's sight.  He has often said he doesn't like to use it unless he needs to because what he might see and what he sees will be with him always.   Maggie hasn't learned that kind of control yet, so she sees the Haunts, so does Mouse but he is old enough to realize  that the children are not the Haunts, but are being used by the Haunts.

   Though I haven finished the story yet, it appears to me that Maggie suffers severely from PTSD and my theory is it has developed her wizard's sight, thus she sees the young bullies like versions of vamps..  In truth their instinct to attack a perceived weak a vulnerable child among them makes them that..  I think if Harry were to look at those kids with his sight, he'd see them as Maggie and Mouse do.. However as we know, unlike Maggie he has control over his sight.  Now what Mouse sees lurking in the wings as the controlling entity might be something else.  Haven't got that far yet but I think it might turn out to be Austin's monster from the Nevernever, perhaps one of the Ebs that escaped the slaughter at C.I. but in a new form.   Given Austin's age in relation to Maggie's age, if he returns, possible future husband for her?

What's chilling would be if The Archive has that much independent agency at all.  I mean, it's one thing to bear a mantle of power, it's a wildly different thing to be the host of an independent entity that might abandon and/or kill you on a whim.  That is precisely why the Winter Knight mantle is preferred over a Coin.

   It could very well have that as a kind of fail safe...  How else would everyone else be protected from the kind of host that Luccio described?  What are the protections against mental illness?  Some severe and violent forms do not show up until the early to mid-twenties...  So what if Ivy becomes psychotic or develops signs of schizophrenia?  Can the Archive act independently if that happens?

   In Storm Front Harry had the sunshine hanky..  After Susan's death, I can't remember who asked him, but Harry replied for him to acquire one again he'd have to be truly happy and obviously he hadn't been since Susan died.  Perhaps having Maggie with him now he may find true happiness again, so I think it is possible in the future he may.

I think you are talking about the long-term dangers of the Archive as set out by the Council's fears.  Im talking about her actual /Power/.   Powerful and Dangerous are very different things, especially in the DV.

  I disagree

page 408 Small Favor

"The Archive was created as a neutral force.  A repository of knowledge.  But what if Ivy's unique circumstance allows her to ignore those limitations?  Imagine the results of the anger and bitterness and desire for revenge of all those lifetimes, combined with the power of the Archive and the restraint of a twelve year old?"
  "I'd rather not," I said quietly.
   "Nor would I," Luccio said.  "That would be a true nightmare.  All that knowledge, without conscience to direct it.."

No she doesn't spell out the Archive's powers on a one to ten scale if that is what you are looking for?  However she makes it pretty clear that the Council is well aware of how powerful the Archive is and how dangerous, plus the dangers of havin

I still dont get your point.  I never said that killing the host would somehow claim you the Archive for yourself, just that a) I disagree with your assessment that the Council has any affiliation or authority over the Archive beyond them both being members of the Accords, and b) the I dont think the Council would actually have the firepower to Take her Down if they were to actually try an all-out offensive to impose their will upon her.

The point is, if Luccio's fears for an out of control Archive comes to pass, someone will have to take it down or the results could be catastrophic for everyone...  Ergo, to whom would that take fall?   Who has the kind of power needed to do it?  Part of the Accords or not, if the Archive became a threat, I am willing to be that Mab would order it's take down, she hates disorder...  Plus the Archive is vulnerable, after all Ivy was kidnapped and held prisoner by Nic..

Given how much they were underestimating her power, I dont actually think they are keeping strong tabs on her.  And between her own powers and likely political the limitations imposed by the Accords, Im not sure how much they'd be able to accomplish on her.

On the contrary,  reread Luccio's conversation with Harry about Ivy and the Archive, she doesn't underestimate the power for a second... Harry on the other hand does, mainly because he is coming down on the purely human side of the equation, Ivy is a very human little girl...  The dangers of that are clearly set out by Luccio, and she throws in why Bob is so dangerous as well..  Though she did not know at that point in time that Harry had Bob.

I think we can be confident that the host cannot voluntarily give it up short of the suicide Ivy's mother used.  I have doubts as to whether even the Blackstaff could take her in a straight fight, and Im pretty confident the Council has no actual authority over either  Ivy Or the Archive. The best they could do is kill her and hope the next Archive that arrises is more amenable to them, which would pretty much make them a full-on Evil Organization of Evil.  That's all assuming the Senior Council is ignorant of the Oblivion War, since if they were they'd not want to make it leaderless for span of years or decades that it would take for the new archive to grow into the role.

I think it most likely way more complicated than you think.  According to Luccio the Archive is supposed to be a totally neutral tool, thus it took part as judge in Harry's duel with the Red Court..  Also if merely killing the host solved the problem of who gets control one would think that Nic would have done it when he had the chance, instead he chose to try and damage Ivy's mind until she willingly came over to his side.  Granted Nic had other things on his agenda as well at the time like destroying holy swords and taking out holy knights..  Remains to be seen as to whether or not the Archive has some kind of "fail safe,"  should it go rouge or otherwise go out of control... Further more if one exists no one knows who holds that button...

 I think everyone will be shocked to learn that Kemmler is Kemmler..

Indeed, that was my point: the family Bargain is still Binding, even if the current individual did not personally and willfully Agree to it.  The fact that the Parents and/or Ancestors agreed to it is enough for the Obligation to be inherited.

  One has to wonder if it works like the Loop-garou curse on the MacFinn family?  Harley MacFinn never had a choice whether he wanted to become one or not, he was just the next poor smuck in the family line to become it. 

Not saying it is the same, but then again the Archive is a bit of a curse, that is why Ivy's mom killed herself she wasn't prepared for and couldn't deal with the burden and restrictions..  I hope one day that Jim goes into the history of the Archive, who was the first host?  Did the original agree for her family for all eternity to carry the burden?  Or was it some kind of punishment or curse for some violation?  Or was it a random thing?  By that I mean knowing that the Archive had to be carefully controlled, Merlin, not to be confused with the Merlin put the names of several suitable families in his hat and pulled out a name?