I just fiddled a little with Scratch 1.4 (http://scratch.mit.edu/scratch_1.4/) on my Raspberry Pi. It looks like a kid could learn the basics of programming using Scratch (the Offline Editor) just by trial and error.
How about a book like Realm of Racket or Head First HTML and CSS?
But keep in mind that programming is fun for some people and drudgery for others.
It's not interactive, but there are plenty of videos available on youtube (for example: this series explains how to make games with python and pygame [0]). Since he doesn't have internet, you will have to download the videos, most likely with youtube-dl [1]. So my suggestion is for you to decide what programming environment is better for him to take on, get the corresponding videos, and next time you visit his family you install him a text editor (I'd suggest Notepad++), the programming language, and give him the videos.
Good luck!
[0] https://www.youtube.com/watch?v=Y7joZ67mC6o&list=PLQVvvaa0Qu...
[1] https://rg3.github.io/youtube-dl/