I've really enjoyed using Ruth Beechick's suggestions in this little booklet for introducing Mathematics to my young children. I think she does an excellent job of explaining how children learn and understand Math. She also lays out a very natural way of encouraging an interest in Math. This little booklet, which can be read rather quickly, also includes activities for learning Math from Pre-K through 3rd grade! In Designing Your Own Classical Curriculum, Laura Berquist recommends using this book for Kindergarten.

Available in a set called The Three R's that also includes A Home Start in Reading and A Strong Start in Language.