I've got some almost pamphlet sized books in my collection, but I think I'd classify my Jacob's Ladder book (Heaven and Earth by Sue Clarke & Hilary Arnold) as having the fewest pages. I mean, it's basically just a 4 sided piece of paper...
The book tells "an ancient Chinese creation myth" (or so it claims - I'm not well versed on those myths). It has very pretty illustrations AND it's a Jacob's Ladder, so it's nifty.