Nearly all, if not all, of these are based on the "china special" which is an Android tablet built on top of the Allwinner CPUs (the A13 is popular in the cheap ones) Ars reviewed a $99 tablet[1] which was pretty funny. If you go to Alibaba.com and search for 'android tablet' you will find a bunch of these. And if you can navigate the Chinese there is a reference design on the Allwinner site which is pretty much exactly what you get.

Put a capacitive touch screen on an Raspberry Pi and boot Android on it and you'll have a better tablet than this I suspect. If someone does a definitive teardown of the specific Walmart model that would let us know exactly which reference design they used.

[1] http://arstechnica.com/gadgets/2010/11/worst-gadget-ever-ars...