My son also had a facility for math that really showed up around 3-4 years old. We worked with objects, like poker chips. Once it was clear that he was having no trouble counting them out, I began grouping them up to teach skip counting and basic multiplication.
DS (now seven) abstracted quickly from objects to equations, so I challenged him by doing addends (e.g. 5+ ?= 9).
We worked on strategies for mentally adding/subtracting larger numbers. We worked on number writing and recognition.
A lot of math can be learned from basic games- around 5 1/2 we began playing Yahtzee. I had him keep his own score, talked in basic terms about probability. I used to toss some coins on the table and have DS count up the money. I would provide strategies for counting quickly and accurately. Like others, we learned about time (starting with digital, then moving to the regular clock), days of the week, how to read a calendar, etc.
There are some fun math games on the iPad. At first I was skeptical about electronics playing much of a role, but once DS had down the basic concepts, the iPAD was a great tool for practice. Currently, DS likes Math Ninja, Mayan Multiplication, Thinkfun solitaire chess, and Pizza Math.
We read some excellent books-- my favorite series is Sir Cumference. I still have them on our shelf.
The most important "thing" (I think) when it comes to math, is to ensure that your child has a solid grounding in how numbers work. For instance, why is 1/2 and 3/6 the same value. Applied problems (I used to make them up on the fly) can help. (e.g. you have 5 kids and 15 jellybeans, how many jellybeans can each kid have if they are split evenly). We used to do problems like this on car rides- DS was dividing well before I taught him the mechanics.
You didn't ask this, but I'll say it anyway- my child had some difficulties because he entered school with math (and to some extent reading) skills that were two three years beyond most of his peers. Math was especially excruciating because he had mastered the K math expectations well before he started K. There are a lot of other threads about this kind of situation, but get ready.
