I haven't found an exact match out there for this set of blocks, but certainly they are Victorian era, my guess is 1880s or so. Though the paper litho is very well worn, I think they're really lovely, and most of the animals on the fronts can still be distinguished. And then on the backs are clever rhymes for each, i.e: The porcupine is two feet long, Covered with quills both sharp and strong. Which guard its body like a fence / of moving darts in ev'ry sense!" I might display them with a mix of the best of the fronts and best of the backs showing! 

Set of 12. Each block measures 2 7/8" x 1 3/4" x 1/2". Structurally the blocks are in great shape, no splits or chips, etc.