This link is to an awesome math facts site, whether you home school or not.
It is put out by Saxon Math, which is the curriculum we use. It's great. Enter what math discipline you want to work on; addition, subtraction, multiplication or division. Put in the highest number you want to use. And how many problems. You can choose whether it will be timed or not.
You then answer the math problems and it corrects it for you when your done.
There is also this link by that has online activities to reinforce different concepts for K-3.
Go check them out. Enjoy!