The comments in this thread kind of miss what I perceive to be the main point of Raspberry Pi. The great thing about Raspberry Pi is not that's it's a cheap enough PC that you can run Python on, it's that it's a cheap device that has GPIO pins and video.

There are significantly cheaper ARM boards than the Raspberry Pi, but to my knowledge none that have video output, or at least reasonably fast video output. Tell the children (or potentially interested adults that have only done software, never hardware) that they need to learn how to use a terminal connected through a serial port, or that they need to learn about cross compiling and other things and instantly the barrier of entry is huge. Tell them they can't have graphics, only a teletype and nobody will care. Let them have a simple thing they can plug a display and a keyboard into and program the I/O pins live while displaying graphical stuff you can see and relate to, now that's something!

Look at Arduino, an expensive and vastly underpowered device, in many ways unsuitable for the task people use it for, but very, very successful because people don't have to deal with all the boring and idiosyncratic low level setup stuff.