I've googled this but a nanny told me I was nuts, so hopefully MNNS have a better idea :)
So as far as I'm aware they keep an eye on the children as well as some basic house chores or washing up, hoovering, putting clothes away while I'm still more or less available/ at home.
So I'd still bath/feed the baby and do more in depth house work.
Said nanny friend said that what I wanted was a cleaner or a nanny but that nobody would do both.