My 3 year old niece, for whatever reason, said she wanted a cinder block for her birthday. While I doubt she'll be able to have too much fun playing with a real cinder block, I figured a set of 1/10th scale plastic cinder blocks might keep her entertained.

I suggest using Skeinforge's multiply plugin to print out whole sets at a time. On my Mendel, I was able to at least 9 at a time, but I probably could have done 12 or more.