When we talk about children here, we generally mean young people who are under 19 years of age and still dependent on you. Many women say that fear of what will happen to their children is one of the hardest things to deal with when they have cancer.
The natural instinct of a parent is to protect children from difficult things and save them from getting upset or worried. It is very common to think that it is best not to tell your child you have cancer. But, however much we try to hide what is going on, even very young children know when something is wrong with the adults around them. If they are not told what is happening, then they can imagine things are even worse than they actually are; and, may end up with fears, secrets or confusion which they cannot share with anyone.
It is best to be honest with your child, using language which is appropriate for their age. Being honest does not mean you have to tell them everything, just enough for them to understand the situation. Allow time for questions at that time, let them know they can ask more questions at anytime and provide simple advice on how they can help you, for example doing the dishes or draw a picture when you are not well.
There is a lot of advice about talking to children about cancer, from those who are very young, to teenagers. The Canadian Cancer Society and BreastCancer.org also has pages on talking to younger and older children.