Biscuit, it is normal to feel scared and hopeless. But you must not give up now.
My best friend's DD was diagnosed with Leukaemia (can't remember the type sorry) when she was 3. The prognosis was terrible, less than 10 % as she had a double mutation, more than once, doctors told my friend she wouldn't pass the week, the day or the night. One doctor even told my friend "I don't understand, she should be dead now" 
.
Today 8 years later, she's a healthy girl, gorgeous, who drives her mother crazy most of the time.
They couldn't find a donor, so she ended up having a self-transplant which worked just fine.
Yes you are facing one of the worst moment of your life. It will be tough and difficult, but you must be strong for you and your kids. Take it one day at a time.
Of course, you have the right to complain and even to share your feelings that it would be so easier to throw the towel and not even try. And you are at the right place here. We are all here to stay with you, talk to you and hold your virtual hand. Right now, you've just been hit by a truck, it will take days to absorb the news, You've just opened the door to a world you knew existed but never really thought about.
My DM has breast cancer right now and I can understand (if only second hand) the roller-coaster of emotions you are feeling. Whenever you feel low, we will be here to help you as much as we can.
Try to occupy your mind (so easy to say, I know). Once you have sorted the wifi connection, why not enrol in a light MOOC (massive open online course)? I particularly like Coursera www.coursera.org/ and Open2study www.open2study.com/. Moocs are free and cover tons of subject . Or listen to some TED talks www.ted.com/.
Or mumsnet like you've never done before. The AIBU and the Mumsnet classics are a good way to spend the time when you are awake at 3am.
A big hug ((()))