While it's incredibly difficult for an adult to understand that a loved one has just been diagnosed with breast cancer, children of all ages are often even more confused.  Dealing with the concerns faced by kids can be a challenge, so parents who are often caught up in the emotion of the moment should consider seeking the advice, support or direction of professionals such as social workers, doctors, nurses, religious leaders, and school teachers.  Encourage your children to talk openly about cancer and express their feelings freely. There is nothing as unsettling as knowing that “something bad” is happening, without understanding what it is. Build in more family time, particularly if younger children are involved. Make sure they understand that they did NOT cause the cancer; explain that cancer is not contagious, and above all, that it is normal to be worried, angry or sad.

Additional Resources:
When A Parent Has Cancer: Information and Resources
You & Me: activities for parents and children when a parent has cancer
NCI - When Someone in Your Family Has Cancer CaringKids 
UHN - resources for breast cancer and caring for loved ones with breast cancer