A very simple JS game I've built with my 5-yr old son
Just clone the project and run it from a local server.
I use to run pure HTML/JS projects with PHP built-in webserver, this way:
$ php -S localhost:8000
Point your browser to http://localhost:8000 et voi lá.
Use arrows to move the character up (jump), left and right. And try to catch the ball.