Prepare any common utilities in advance: a manager that starts the game loop, switches to game over, enables restarting, etc. Sound settings are always useful.
Create the repo, then try to build and publish a Hello World app.
For the 9-year-old, tell her what to expect from the development process. I assume she can dedicate only a couple of hours? If so, plan the scope accordingly.
DON’T FORGET TO HAVE FUN!