There really isn't much to add to what has already been said. The very fact that you came on here to look for help says a lot about the kind of friend you are.
As a mother I can honstly say there is nothing in the world as bad as seeing your child sick or in pain and I feel for what this poor person must be going through. As someone who has lost many people in their life...not a child touch wood... I would say the most important thing is to be alert for when they want to talk about it and when they don't. People react in different ways and by and large others try to avoid the subject like the plague but sometimes it is a relief to talk to someone about the anger, fear, pain etc.
Just be open hun and be there. If you need to talk, to rant, to scream and shout we are here.