The term child pages refers to a group of pages that are beneath the same parent page.
(E) Child visible in navigation
Hide the child pages from an in page navigation layout (where configured in a template) for website visitor views.
(F) Child visible in CMS navigation
Hide the child pages from an in page navigation layout (where configured in a template) for CMS user views.
(G) Default child URI prefix
Set the URL format for pages created as children of this page. This is useful when you want to shorten the URLs for a certain type of page, ie: news stories - when the news section is at www.domain.com/section-1/section-2/news/news-story-title then, by setting a short URL as /news/ all news stories can have the URL www.domain.com/news/news-story-title by default.
(H) Default grandchild template
Set the template for any children of the children of the current page (!) This is useful when creating sections that will have levels of content created by users with reduced CMS permissions.
You must Save your changes for them to take affect.