squishy - great post that - I usually do say that there are alternatives to HL, but currently on holiday so less time for posts!
But I agree with all you say, especially the not panicking, some of our funds haven't done as well as others, some do drop, but overall I think the total will beat any bank account, especially at present, which is what matters. And a long term view is definitely necessary.
We are totally self taught, just bumbled along in early years, learning from experiences eg not putting all eggs in one basket (or 1yrs allowance in one fund which then bombs in dot-com bubble - fortunately a v small portion of my portfolio now).
Good luck Op, S&S ISA definitely the way to go for kids at moment, your DC will thank you when older I am sure, whatever you choose.
My DC already had a healthy pot at 15/17, then got an inheritence, which is being drip fed in. Eldest over 18 so has full allowance, his pot is now growing at an alarming rate.