How to create a git project(s) that are based on an up-to-date version of another project?

Question

git

Greetings!
The company has a repository that stores a basic template for websites. It is sometimes finalized when it is necessary to add the same functionality to all our sites, fix a bug, etc.
And now the task arises in which we need to create child templates that should be inherited from the base one, but expanded with additional functionality (new files are created , dirs).
How can I make it so that I can make changes to the base template, then switch to child ones, quickly and easily apply changes from the base template to them, and then continue to expand the functionality at the level of only the child template.
Git projects look like this:

1. Base Template
   
2. Child Template #1
   
3. Child Template #2
   
4. Child Template #3
   

Interested in implementation only at the git level

Answer 1

Fork child raps, sync with master when needed. How to sync:
https://help.github.com/en/articles/syncing-a-fork
Please note that the main repository is not origin, but upstream.