'Don't understand those of you who pay for stuff yourself then reimbursed from parents - why do it this why?'
because it's what works best for us
'you may forget to write down something'
Always possible, I'm pretty organised so it's only ever going to be the odd thing, not really a problem.
'Two - I personally can't afford to pay for kitty costs out of my salary once bills etc have been paid (things like sains petrol hair cuts music lesson etc)'
Luckily I can. It's only really a matter of £200 or so, refunded at the end of the month and then pays for the next month etc.
'Is it not easier to have a kitty purse and just use that'
For me, no. I find with a kitty purse that I forget to take it or they forget to put money in it. If I'm doing some shopping for them I'll often do mine as well, then rather than paying with two different purses and getting two lots of change and getting all mixed up, I just pay for it all and then use the receipt to charge their stuff to them.
'And what could happen in one extreme case - years ago a nanny I know used her credit card and got it paid each month - handed in notice and parents were very annoyed and basically made her 6 weeks notice hell and parents refused to pay the last month bill that came a month after she left - she got stuck with it'
This is obviously a possibility. The thing is though trust is a two way street. They trust me with the lives, safety and happiness of their 4 small DC, they trust me in their home, they trust me with their money (no receipts/proof ever asked for). I think I should trust them to reimburse me £200. If they gave me a £200 kitty at the start of the month or a credit card to use, would you think this is ok? So ok for them to take a chance on me, but silly for me to take a chance on them?!
Ultimately it's what works best for us.