Here is a collection of free online math games from PBS. Most games are for elementary kids.
It was Pi Day two days ago. I was able to find some very interesting websites that are math related.
First, is this great infographic http://ow.ly/j3yWb It is very big, probably not reasonable to print out at home. But I was able to print just part of it for my son.
Next, I found this article with 22 free websites for Math teachers, all are Pi day related, such as Pi day activities, challenges, fun facts. While it is for math teachers, parents can also find it very helpful. http://ow.ly/j3zt6.
Lastly, here is a picture for everyone. I did not create it. I found it http://ow.ly/j3zIt. Have fun with math!