What can they do with it? From the little I understood, it sounds as if it could be of interest to 12 yo
It's very much about getting people to actually write programs with languages like python or scratch.
There are plenty of online tutorials and guides etc, I'll put in some links at the bottom.
It's also really good for learning about electronics as well and actually trying things out in real life.
It's also a great way to cheaply learn how to get computers to control things. For example if your dc have any interest in photography/video or robotics then this is a cheap way to get them to start exploring those areas and how they can be controlled with a computer.
Obviously you will need to buy extra things, but again these are all pared down and quite cheap - at least compared to the price of lots of fancy equipment.
Here is a video tutorial of someone writing a game:-
www.youtube.com/playlist?list=PLgyU3jNA6VjS3ij6ZXbb2x4GdEP3bAWzO
Have a look at the video on this page of the raspberry pi website:-
www.raspberrypi.org/what-can-you-do-with-a-raspberry-pi/
For my dc, the interesting bits are what they show in the video from about 1:56.
There are plenty of online resources, for example here is one by a teenager that has done quite a lot:-
www.raspberrypitutorials.yolasite.com/
Here is a video tutorial of someone writing a game:-
www.youtube.com/playlist?list=PLgyU3jNA6VjS3ij6ZXbb2x4GdEP3bAWzO
These people also do some good tutorials:-
pibeginners.com/
This guy has a whole load of tutorials, this one is on how to use the pi to control a motor to turn the wheels on a model car:-
And a pi controlled remote control model car:-
These people also do a lot of tutorials as well:-
pibeginners.com/
and you can also get good ideas here as well:-
www.adafruit.com/blog/