I don't know where you're located, but if it freezes at all in the winter, I'd really recommend not fooling with cinderblock. Reason being, you would have to build/pour a good solid footing, wider than the cinderblocks and deeper than your maximum frost depth. This is MUCH more work and expense than you wanna get involved in, trust me.
Even in a frostfree climate, you need to have a very well tamped base for the block wall, evn if it is just 2' high, because otherwise the ground can erode/settle unevenly under it.
Frost heaving, or uneven erosion/settling, will cause your wall to get all wonky and even if it doesn't collapse it will no longer mate properly with the rest of the building and critters will be able to get in.
I don't really see any advantage of cinderblock knee walls unless you are on a deep foundation or poured slab, anyhow -- predators can easily dig underneath.
Good luck, have fun, be real careful with any attempts at building walls,
Pat