@liz27 - welcome. You will get through this. I was diagnosed with ILC in Dec 2017 just in time for Christmas. Those first couple of weeks, comprehending what it meant and having the tests and scans were a nightmare of tears and disbelief. I also had 3 kids, two still in primary school, who knew that my sister had died from this before they were born. Lumpectomy, mastectomy, chemo and radiation followed over the next 9 months. I have always told my kids that I would not hide anything from them (but I don't tell them my darkest fears, of course). I do let them know when I am anxious but also that my anxiety is not necessarily based on reason. Kids can pick up on things but it's secrets that are scary. I won't say that everything for them was plain sailing. Of course it wasn't. They all struggled at different times and those struggles had to be addressed but on the whole, I am very proud of how we navigated that year. So, my advice is don't hide things, and don't underestimate their ability to rise to the situation.
You'll probably find that as treatment starts, your mind settles a bit as you have a plan of action but at some time in the process, you may find that you need some counselling. For me, as for many others, that came towards the end of active treatment.
Be gentle with yourself. Your world has been knocked completely off balance. Use your support network as you need to and don't be afraid to ask for specific help. A freezer full of meals might not be the best option when you really need help to get a kid to after-school sport.
Take care