"Most" games these days are not coded from the ground up. As you have said allready there will be tonnes of tools/utils that are used. The games designer will in most case just be using these tools.
There used to be one called Virtools that was used in some schools and "teaching" games were created in it. I think the company has been bought out now
http://www.3ds.com/products/3dvia/3dvia-virtools/
Basicaly you just drag building blocks around to build up a level. Add your textures and sounds. Then if you want go hardcore and add logic/ai and scripts for complex stuff.
A simpler version of this ^^ is what you want I think so the kids dont get too bogged down with code as it will cause most kids brains to just give up, but everyone can cope with dragging boxes and drawing lines.
The Unreal Development kit and also the Crytek dev kit are similar but not as generic as they have target game types in mind. Also the GUI/tools dont seem to be as polished. You should be able to get a 3d animated model running around controlled by the keyboard pretty easily but anything more than that will get into the hardcore stuff. The final diagram of your game ended up looking abit like an old school circuit diagram.
The only other dev kit I can think of is the XNA suite for windows. But I dont remember it being as mature as any of the above.
In terms of languages there used to be one called BlitzBasic that worked on windows and was perfect for teaching the younger people to code, again though it was primarily code with very few graphical tools.
