What a strange image people in your office have of people wfh Wowfudge 
I have no more nor fewer showers and baths if I am at home, in the office, presenting training, attending meetings or any of the other visits and tasks I do in my job. What a weird idea!! I mean, when I wfh, I might not see anyone else - my boss certainly wouldn't drive over to my house without notice - but I would feel odd if I hadn't had a wash nor cleaned my teeth. You seem to be confusing wfh with being homeless (though many homeless people still clean their teeth every day....) 
Oh, and I think it's important to be very structured in your finishing time. It's really easy to do 'just one more thing' and find yourself still working at 8pm.
Now this ^ I do agree with. I know if I send an e-mail round to the team about something I'm stuck with at 9pm, I will get answers.....
Another question I've been pondering:
I have to complete between 6-9 hours a day (flexi). Is it generally considered ok to do the bulk of my hours e.g 9-3, then break off (collect children, await return of husband), and finish off the remaining hours if necessary eg 5-7pm? Obviously it will depend on the company but is that considered normal?
I do know that I can't work outside the core hours of 7am-7pm.
That is going to depend on your company, and also your line manager. I would say 'yes' - as that is the point of the policy, to give employees flexibility. However, this comes back to what you do and keeping track of what you actually do in reality. Our "policy" also says you are only supposed to work between 7am and 7pm, but out boss is more than happy with us doing some of our day in the evenings as she knows it can work for us, so I have my own document of actual hours worked, and then fill in a - ahem - shall we say 'rather adapted' version of what I have worked, so it ticks the right boxes on the time sheet. Ultimately I know I have done the hours well, usually more than and for a lot of the time, it makes no odds if I am working at 3pm or 9pm. If anyone every 'reported' seeing me out picking dc up from school at a time I said I was working, I still have the note of what I actually worked that day and wasn't able to log on the timesheet. Never have been asked for it, but it is there, 'just in case'. This will depend on your own job though.