I wonder what life was like for the IVY when it came to monsters only kids could see....imagine a oblivion story based on destroying or altering this book that the carpenters wrote, it could be the reason that ivy actually chose to be the arbitrator for the dual in death mask. remember that Molly was 13 or 14 at the end of her child hood but still a child.
What, like a child-eating phobophage actually trying to attack Ivy? It would probably be dead before it even realized it had made a huge mistake, unless she valued leaving it alive to warn its peers not to mess with her. There's a pretty big gulf in how directly powerful the antagonists for a children's or YA series can be vs. what it would take to threaten someone insulated by the full power of the Archive.
The targets in the Oblivion War that are anchored to reality by human knowledge are the really big fish of the Dresdenverse. As far as Ivy is concerned, if childhood phobophages merit her consideration at all, they're probably more on the scale where she's content to see knowledge of how to fight them spread around. If working to get mortals to forget the nasties was the best course of action for everything, Lara would hardly have personally engineered the Stokerlypse. Frankly, if the things that target kids were so powerful as to be targets of the Oblivion war, the post-industrialization population boom probably wouldn't have happened on account of them eating the extra humans.
Besides, even if Ivy did want the Carpenter kids' book gone, destroying it would do little when there are still young kids around the house aware of its contents and able to recreate it. Even if Ivy were to personally take a role in destroying written records - and everything we know about the Archive's compulsive caution says working through Venator cutouts makes more sense than exposing herself to unnecessary risk by acting personally - the time to get that book would be after the last child has grown up.