In the link sugested the source codes are ready working Visulal C++ projects. Just follow a few instructions provided and 7yo child can do ( just true version of MS Visual Studio required)
Compiling a few samples you find online isn't programming. Any untrained monkey can do that if you just make the compile button big enough. I could probably put together a kit-car given enough time, but that doesn't make me a mechanic, much less an automotive engineer.
It sounds like the your kid will turn out alright whatever he ends up doing.
He's into programming... Clearly he's gonna... 
I started making games when I was 12 using GameMaker, which is kinda like Unity but 2D so it's simpler.
It's nice since you can get results much faster and more visually than with the other engines and a lot of the heavy weight stuff is abstracted away.
It helped me a lot anyway.
The only catch is that it now costs at least $50 if you want to do anything bigger than Pong with it, so if money is an issue I'd recommend him to learn C# first and then afterwards learn Unity.
EDIT: And also, and this may sound obvious, regardless of what he chooses, praise for even the simplest looking accomplishments is nice since it's actually pretty hard, so when he excitedly shows you a ball that bounces around or a square you can move with keys, congratulate him on it.
That's interesting!
I did the exact same thing, and maybe GameMaker wasn't the best, but it definitely took me a step further into the world of games and scripting.
