ZCO takes place in the mid of November. The registrations start somewhere around October. Once it starts, you should be able to register in the official website here: http://www.iarcs.org.in/
This is the official Indian Computing Olympiad website.
Firstly I would like to congratulate you on giving your son this exposure at such an early age. It is really inspiring!
Yes code.org is amazing and it is really great to hear that he is progressing with ease.
Next he should pick up some programming language. And he must choose between C++, Java or Pascal(these are the only ones allowed at the IOI as of 2017). I would suggest C++.
I don't think it is required to make him acquainted with Scratch or Tynker.
Yes there are several courses to learn C++ online. I will try to post some good links here as soon as possible.
Once he is comfortable with programming in C++, the Competitive Programming Playlist is the best place to practice and learn the most important algorithms. It has all the best possible tutoria...
UNITY 3D is a very powerful game engine. You can make really awesome games with it!
You can have a look at these official tutorials by Unity 3D: Modules. These introduce you to the basics of game development and using Unity 3D. The best part about the tutorials is that you learn by developing games rather than just hearing hours of lectures doing nothing. At the time I took these tutorials there were only the first three modules. Now they added more. The projects are really fun! The tutorials have been presented really well. Very easy to follow!
The videos are already ordered. So I would suggest, watch them one by one starting from the first one. Also don't forget to check out Competitive Programming Playlist . This is a much in depth playlist with a lot of problems for practice and quizzes to test your understanding. I would highly recommend this playlist!
I would highly recommend you to go through the Graph topics in Competitive Programming Playlist. They are the best resources I can think of, that are available on the internet. I myself learnt Graph Theory from those resources. Go through it and feel free to ask in case you are stuck somewhere.
This is a really great problem. Here are a couple of hints to get you unstuck. If you are still unable to figure out the solution let me know so I can expand these hints.