Hi @Mantis,
I have four kids, 18 - 10, with an even split of gender. Two are my nephew and niece who we're raising after my sister died from BC 17 mos before I was diagnosed. They're quite traumatised, so it was very difficult and needed some delicate handling.
Broadly speaking, first up was lots of reassurance. I found my cancer early (unlike they're mother) and had it whipped out fast, so I hit the stats hard when talking to all the children, and my nephew (12) was particularly comforted by the fact that it was "already gone" the day after my diagnosis.
I hid my distress from them all. I cried a lot in the first month. I mean a lot! So there was camo crying in the shower, a lot at night, out walking and while they were at school. It actually doesn't do your kids any harm to see you cry. In fact I believe it can be a good thing as they see it's OK to show emotion and develop empathy. However given my family's set of circumstances (my womb kids lost another aunt as well (my husband's sister with whom they were very close) to a brain tumour two years earlier) I did not want to be distressed in front of them.
I made an effort to keep conversation as normal as possible, rules & discipline the same, routine etc. This became harder when I began chemotherapy. There were a lot of people dropping food off, coming in to help and it was harder to maintain the normal routines. But you do your best. As @Sister said, you have to not sweat the small stuff. It's not the end of the world if the kids go to school in an unwashed shirt every now and then! Mine became more independent and I've let that continue rather than resume all I was doing for them before.
I disappeared into my own head somewhat and a couple of times realised I hadn't communicated with the kids what was going on with my treatment. They fill in the gaps, often incorrectly, and this was causing them worry. So endeavour to communicate age appropriately so no one is left wondering. A bit of one on one time so they can open up without fear of sibling mockery is handy too.
My eldest, a son, didn't say much but a few times rose to the occasion and helped out magnificently making me very proud. My 15yo daughter needed some extra cuddles on the couch in front of the tv. The youngest, a girl, needed information so she could understand, and the 12yo needed to know the routine and structure of each day. They're all different so I'd advise noting what it is they require individually and delivering individually.
I hope that helps! K xox