It seems like GNU/Linux would probably be much better than Android. With GNU/Linux there is full access to the OS/device and they could fully tinker with it. No Internet connection required for LibreOffice. Raspberry Pi is relatively inexpensive.
A rooted Android gives just as much power. With the added advantage of having the biggest developer base in the world (in case you dont want to muck about /proc or low level).
In addition, buying few 10 inch android tablets using MTK chipsets is just a click away and less than 100$ shipped - with working 4g, wifi, camera, etc etc. Getting the same to work with GNU/Linux is going to be a pain.
I think that there is a cultural issue to consider as well. Android culturally tends to be a locked-down platform that takes control away from the user. GNU/Linux is about technology Freedom. You can unlock Android devices with a significant amount of effort, but it would be better to start with something that is fundamentally open.
It seems like tablets would break easily, where it's easier and cheaper to replace small screens on Raspberry Pis.
