Follow the these steps to generate a list of the child pages of a current page and the further descendants (children's children).
1) While you have a parent page open--
- place the cursor where you'd like to insert the list of child pages,
- use the keyboard shortcut Ctrl + Shift + A or Menu option Insert > Other macros to select the macro for "Children Display"
2) Find and click on the Children Display macro under the "All" or "Navigation" folder
3) Check "Show Descendants" and select h4 as Heading Style. You may also experiment with the parameters of other fields until you are happy with the result in the Preview box. Press Save.
4) A list of the titles of the child pages of the current page will be generated, hierarchically arranged the way they are displayed in the Preview box. The Child Page Display is synched with any future change you will make with child page titles and does not need manual maintenance.
Resource
Atlassian support > Children Display Macro