Oh man - I'm so sorry for your dad's diagnosis. It is so hard.
Here in Minnesota, we have an organization called Minnesota Angle Foundation - it is specifically for families facing cancer ... with the PARENT the one with the diagnosis. Our family went to a series that was for the parents and the kids. The kids went and did activities with the kids, and the parents when and did activities with the other parents and adults involved.
I know of a similar organization in St Louis - it's called
Cancer Support Community Kid Support/Families Connect. For parents and children up to age 16.
Anyway, ours was great. It was called Facing Cancer Together. We met once a week for 6 or so weeks. My child had a great time, and he got a lot out of it. He got to talk to other kids with a parent dealing with cancer. Then, my son went to cancer camp, which was for just the kids. It was a daylong camp for pre-teens and an overnight camp for teenagers. He can't wait til he gets to go as a teenager. We also go to some other events periodically. He doesn't talk to anyone else about cancer... Just people through MN Angel. Makes sense, right? The other kids really don't understand what it is like.
So, you might consider looking around for something like that. You might even be able to get some help from an adult at school or maybe from a trusted adult.
So, I typed in a quick google search, and this site popped up. Maybe there are some good resources here.... http://www.oscook.org/support-groups.php
Good luck. This is so hard. I hope you find something that will help you with all of this.