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!
HTML and CSS are the two fundamental languages of the web: HTML creates the content and structure of a web page, and CSS controls what it looks like.
Some courses teach both together; some separate them. Either way is fine!
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!