Here are courses for digging deep, organized by language. Each includes an explanation of what that language is useful for, options for free courses, and documentation (think the dictionary and/or official manual of the language). If you need help picking a language or choosing a course or project, just ask!
Python is a language designed to be easy to get started with. It can be used to create games, data visualizations, web applications, and scripting in other software. (Reddit is written entirely in Python, and so are parts of Wikipedia, Amazon, and Instagram!)
Code.org has lots of intro-to-coding activities with fun themes!
(Awesome bonus: all of these activities will run on a mobile device like a phone or tablet!)
Scratch is an amazing platform for creating games, animations, and much more!
The Scratch foundation also has a free curriculum available in many different languages, and there are free online courses available through Pluralsight and edX, and the Scratch Wiki can be a fantastic resource!