My 4yo and 7yo daughters are enjoying playing with numbers at the Daisy Maths site.
From the site: DaisyMaths is a program designed to help young Australians to enjoy learning maths. It is specially made to be free, fun, and informative for Australian kids aged 3-12. DaisyMaths was originally designed by an Australian professor, Professor Myles Harding, to help his young daughter (Daisy) understand the basic concepts of mathematics.