Teaching math with the dot cards works until the child is about 30 months.  After that they have probably learned the symbol of 1,2,3 etc.  instead of the real value of the dot cards.  You can still teach a young child heaps about math though.  We started a reading program with Doman method for our 14 mo and 3 year old at the same time.  The 3 yo was less interested but still picked it up.  Just sit in the middle of the room and show word cards, and the kids will pick it up.  Always stop before they want to stop and go fast fast fast.  never force them to watch.  Its all so clear if you read the Doman books,How to teach your baby to read, math, encyclopedic knowledge.

The 3 yo is now 6 and reading way above his peers, and he got a small program.  ANY reading program will be good, but if you can do it specifically, organized and consistent it will be very good.  You just have to show them, the brain does the rest.  Reading is a neurological function not an intelligent function.  Its all really clear in the Doman books.

Good luck and get busy.  It will be very rewarding as a parent.