Play-dough and modeling clay are great tools for introducing patterns and fractions to preschool kids. Have them cut out shapes, then move from simple patterns like "circle square, circle square," to more elaborate patterns like "circle square heart, circle square diamond, circle square heart, circle square diamond." It is amazing to see the patterns they will come up with. For fractions, make the proverbial pie, and parcel out one fourth, then two fourths and show how two fourths is equal to half the pie.