As a homeschooling mom and a certified teacher let me congratulate you on this endeavor. It will be maddening and rewarding and very rarely at the same time. 

As to your question, you are going to want to be a "coach" to your children. You will add them to your roster as your students. Khan has put together an amazing resource bank to help teachers know how to best use this site. I am adding a link for you here:

https://www.khanacademy.org/coach/resources

There are so many facets to this. You can skip around and just hit the things that look good to you, or go through all of them and become a master user :-)

Good luck to you, krystlemc!