Supposedly the easiest game engine out there. Never used it myself though. It's not free, but only $15US, so save your lunch money for a couple of days and you have it.
Game Maker, very robust 2d engine, also capable of 3d. free. no licensing required. uses it's own scripting language but it's based off of C++.
get it at www.yoyogames.com
for beginners they can use simple drag and drop programming, and as they get more advanced you can use the built in scripting language to do more.
Its a excellent 3d modeling tool and the game engine is one of the best that i have used, all the Physics lighting and particle systems are absolutely excellent to!
A basic breakdown off all the features are **broken link removed**and its free and open source too
I Can't wait for them to release the 2.5 the alpha is brilliant but a bit buggy at the moment
I will take a look at the ones mentioned.
We only have till the end of term. So in this case simple to use will win. With luck it will turn encourage him to make an effort and do more complex work.
I will be happy if it teaches him to think sequentially.