Babies have the ability to learn true quantity beginning at around 3 months of age. They lose this ability somewhere around 2 1/2 years old. I have tried to teach my babies true quantity, addition, subtraction, and division. I was really consistent for a period of time, but I tend to be more dedicated to the reading programs.
That being said, it is really easy to teach babies math on a daily basis. I have a CD that teaches basic addition through song. I got this for my older children, but the babies seem to learn whatever the older children are doing anyway. I sing a simple addition song to my children. It goes like this:
1+1 is 2
2+2 is 4
3+3 is 6
and so on. It goes up to 10+10 is 20. The fascinating part of this is that I can ask my child what 8+8 is, and they will quickly say 16.
I took this a step further just last week. I asked my daughter if she wants to play M&M math. I sing the adding song to her and demonstrate the quantities with candy. Then I teach her subtraction and she gets to eat them. We start with 10-1, then she eats one and we determine that there are 9 left. This is fun and interactive way to expose toddlers to math. For people who are more health conscious, they can use raisins.