Great Schools.com has a great article on what your child should be learning about math in preschool.

For this post I will just extract the things you, as a parent, can do at home to reinforce math learning in preschool. Have fun and teach at the same time!

1. Show how math relates to daily life. Involve them in measuring ingredients when you cook or in figuring out if a container is big enough to hold their toy cars and trucks.
2. Play board games using dice or play money. Help your child count out the spaces to move his piece on the board. Play simple card games like Go Fish.
3. Count things at home and on the street: cars, books, toys, silverware. Count objects in book illustrations.
4. Call attention to different patterns and shapes: plaids, polka dots, paisleys, and triangular and rectangular shapes in the sidewalk.
5. Use terms such as above, beneath, level, larger, smaller, and equal, and words such as horizontal, vertical, perpendicular, and parallel, to describe things you see. You might ask your child to bring you the smallest cookie or to find the book beneath the large table in the living room.
6. Take your child to the supermarket with you and involve her in comparing prices.
7. When you balance your checkbook or pay bills, explain to your child what you are doing.
8. Take your child to the bank with you and let him watch you count money from the ATM.
9. Weigh and measure your child and make a chart to record her growth.
10. Buy a set of hardwood blocks for your children to build with (look for a secondhand one if new ones are too pricey). The educational benefits of blocks are unlimited; they will be one of the best investments you make.