Page Post Structure

I want to assign posts to pages. I have the Page Links To plugin.

I am able to do this with a parent page, but not a child of a page. The structure that works for the parent page is:

Page links to https://site/category/parentpage
I create a category named parentpage
I post to parentpage category

But I am unable to duplicate this with a child of a page.

FYI. In my testing I noticed that if a parent page name is more than one word, the path can’t be found. Example: page links to: parent_page can’t be found, but if I just name it parent, it works – but only in the parent, not in the child (with one and/or two word page names.)

Summary:
I want to have

Page
Child of Page>Posts Here

Anyone familiar with this structure?
Thanks!