I think all the advice here for Keeping and Topsy is really, really sound. I can't add much.
As regards telling children about cancer, my dd was the same age as smee's ds, and our approach was similar. It is important to tell them about things in advance, I think (eg hair loss) so they are forewarned when well-meaning adults start saying things that they can hear. It may be a good idea to take them to a check up or bcn appt - just one, which you expect to involve no undressing or difficult talks, so they can imagine where you are going at other times, and realise that it is all pretty normal and unthreatening, and see how many other people are going there too.
Telling their teachers is a good idea, as they may mention it in school. My dd did chat to her teachers about it, they were prepared, and they were fabulously helpful and reassuring (it did help that her class teacher's Mum had had bc and was fine 10 years post treatment).
I also had a wig which was never worn as I looked like a man in drag in it. I just wore scarves, even to business meetings and it was fine. At our hospital there is a wig specialist who comes in, and she has a good selection of wigs that are NHS subsidised. My contribution was about £60, I think. But don't let my comments about my wig put you off getting one if you want to. There were many, many women wearing them in the chemo unit and you really could not tell. I thought I was being hard done by as I was the only person to have lost her hair - the head chemo nurse had to give me the heads up.
I'd suggest the way to get the right wig for you would be to take along a friend whose judgement you trust when you go for the fitting. Good luck!