Impact on kids

What @kmakm said... My kids were 11, 12 & 15 at diagnosis and they have grown up knowing that they never met their auntie, my sister, due to breast cancer so it was always going to be an issue for them.  I won't say we've not had anxiety problems but really, they've done pretty well.  We told them from the start, that we wouldn't keep secrets and that they would always be the first to know anything.  I also talked to them about the things other kids, and adults, might say such as "your Mum's going to die" and that they should tell me or their Dad if anything was said that worried them.  I have always been honest too, about how I'm feeling.  They have each at different times, asked me questions - as @kmakm says, usually in the car or while walking.  Remember that if your child gets the slightest wind that there could be secrets, she may build them up to be monsters.  I would also be inclined to advise her teacher, it someone at school.  You can tell her that such and such needs to know in case she needs to talk to someone, but you can instruct that person not to bring it up with your daughter.