When working on AEM, you will need to create a hierarchy of pages depending on your content.
A parent page is any page that sits on the top of your hierarchy such as, home page is the Parent of About our school, Supporting our students, Learning at our school and so on.
A child page is the one that sits right under the Parent page, could be called the second level page and so on. Child page could be any page that you create under another page such as, Learning from home, Creative arts, English, Languages and so on are child pages of Learning at our school page.