It's natural for families facing a cancer diagnosis to be upset and worried about how they will deal with this crisis. Families with young children or adolescents may have additional concerns about how their children will cope with the uncertainty produced by a cancer diagnosis. 
"Talking to children about your cancer can be a very difficult thing to do, and may be upsetting for both you and the child. However, involving children in the situation and letting them know what is happening can be very supportive to them and can help them to cope better with a parent's or grandparent's illness." 
"All children experience guilt about their possible causative role, grief and yearning for lost parenting from both parents, fear for themselves, and anger and resentment about being abandoned or shunted aside. This latter reaction can be quite realistic, as young children are often sent away and are almost always bypassed in the illness communication network. Therefore, fantasies replace fact, and, as child therapists have long known, these are more tormenting than even a grim reality." 
"Honesty helps children establish and maintain a bond of trust. The truth, even when it is painful, is vital. If a child learns of a parent's deception, they will have a problem being comforted later by words/actions wondering if the parent is telling the truth. By being truthful, you can also feel assured that the child can be guided to accurate, healthy and hopeful interpretations of events and you can help them to learn coping skills."