Everyone apt enough to use a computer understands what a parent-child relationship is.
Experientially, I would consider the usage of the term "parent-child" in abstracted contexts to be fairly technical. If your audience is non-technical, I believe this usage will be confusing (at least initially so).
As a general principle, it's often advisable to rethink the design when technical concepts start "leaking through" into the user interface. I would say that a design should abstract elements in such a way as to convey relationships without relying on terminology.
I understand that, from a power-user perspective, it's highly desirable to reduce the number of steps in a workflow, but in this case, it's at the expense of clarity. I would suggest keeping the children elements (poems / chapters) within their respective parent elements' view (the book view), & use an element such as breadcrumbs to provide a sense of spatial awareness of their location within this object graph. The idea is to only show elements of the same type within the same grid at any given time.
If a redesign is out of the question, consider using terms specific to the current context. E.g., "Show / Hide Poems" or "Show / Hide Chapters". If you go that route, definitely make sure that parent / children elements are clearly differentiated.
Hope that helps & good luck!