It's great to hear that K so far has been successful & happy place for your son. I personally would not push for more math at this time. When my DS16 was in the same situation I didn't. If he wants more challenging math, I would informally after school him. There are a lot of ways to challenge him at home.
At this point in K your son is learning a LOT of new things. All parts of his life don't need to be challenging, new and difficult at the same time. It sounds like he is enjoying these new things and math is only one small part of the K curriculum. You son has YEARS to learn math and if you did push for more challenging work it's quite possible it would still be "easy" for him.
Despite my suggesting that you don't need to push, you can still bring this up when talking with the teacher. Making the teacher aware that your son loves math and can do math way above grade level is still a good thing for the teacher to know.
