What do you tell them?

There was a post on the acor site today from a man whose wife has MM and they have a 9 year-old boy. He is worried about the future, wondering how to prepare for it, and worried how all this
is affecting their son. One of the hardest decisions to make, I think, is how much to tell your kid(s). Olivia was almost 9 when Tim was dx'ed. He was hospitalized in intensive care with sepsis and she was not young enough to hide all this from. He was going to lose his hair. He was really sick and came home painfully thin.They say that if you leave it to their imaginations, they will worry more and think of even worse scenerios. Besides all this,
I am a ridiculously honest person. I can't stand lies. I don't want to teach my child not to trust
me by lying to her. On one hand, this rotten turn her life took was cruel and I wanted to protect her so much. On the other hand, I did not want her screaming at me years from now because she was full of regrets and angry at me for not telling the truth. I told her but left out the really scary stuff. It was several years before she came into my bedroom, after being tucked in, crying because she was afraid of something happening to Tim or I. I told her this was way too much for a little girl to handle and to let God take care of that one. I assured her that Daddy was doing great now, etc. We usually try to go to Tim's doctor appts. when she is in school and not even tell her but sometimes, we have to arrange a play date or school pick-up for her and we had to do that this last time. She asked me why Tim had to go and I told her they check his bloodwork every couple of months. I don't know what Olivia thinks as far as if he is cured or what. The problem is, you do not want to make them any more curious than they already are. You've got to say enough to keep them from wondering or worrying too much but not enough to completely traumatize them, of course, or have them running to the internet to fill in the blanks. The first time I looked up MM on the internet, I came upon something that said that a person would live about 2 years if dx'ed at stage 3. I shot off my chair and screamed. No one was here. Kid in school, husband in hospital, but I lost my mind. I did not want to tell Olivia NOT to look MM up on the internet because if she had not thought of it already, what do you think she was gonna do after a warning like that? Recently, I realized that she had probably already done this by this age so I gave her a vague warning that there is a lot of outdated information out there about MM. I always tell her she can come to me and talk about anything. I ask her how things are going for her at school, and in general. She always says things are good. It breaks my heart what has happened to our little girl though. It's so damned unfair.
She has been such a trooper but I fear the lasting effects all this could have on her. Kids are the first thing we think about whenever something happens. You worry about them until you take your last breath on this earth. They are the biggest blessing in your life but also the focus of the biggest fears you have as a parent. Olivia is almost 13.
I have a feeling that some REALLY hard questions are coming. What the heck am I going to say to her? I do not want to ruin any chance of happiness that she has. I also don't want to lie. Life in this day and age is freekin' hard enough. I think this is Tim's biggest sadness about his MM. How it affects his daughter, me, his parents. I beg God not to take him at all but at least not while Olivia is SO young. Well, I gotta go watch "The Big Bang Theory" and get some laughs.
Any advice about handling this with kids is gratefully accepted.