Found this interresting gem:
kid-proof/ruggedized tablet/netbook
http://www.peeweepc.com/store/pc/viewPrd.asp?idproduct=70&idcategory=2#details

This would work fantastic with Ubuntu MID/Remix or Android!

Unfortunately local suppliers able/willing so suplpy windows-less machines are few & far between.
Some stores would charge you an addtional fee to remove the win-OS (they don't quite understand...)