My contract states one night babysitting a week (can be overnight) any overtime paid at £xx per hour.
That said, if my employers are good to me, then I will do extra babysitting and not charge, if I have no plans of course.
I will also watch the boys on the weekend for 30 mins while MB goes for a shower if she is on her own and I am having breakfast etc. But I have always had seperate accommodation so doesn't happen often!
My bosses are very generous with time off, boys go to GPs for a long weekend every 3 or 4 weeks and GPs come here for a long weekend in between, when the boys go to grandparents, I take the boys up to London on Thursday afternoon, meet GPs who then take them up North! Once the boys are safely handed over, the time is my own. When GPs come down to us, they walk in on Thursday afternoon, I hand the boys over, go catch up on jobs that are not easy with the boys around (spring clean their bedroom/playroom (if GPs take them out) sorting clothes, batch cooking or finishing ironing) or shoot off for the weekend! once done, I am free until (generally) Tuesday morning when they leave.
They never ever quibble about paying me for this time off, so if we go on holiday, I don't tend to charge for travelling days if they fall on a weekend (which ordinarily I would whether or not I was working!)
It is all about give and take!
If you would like your nanny to do the things you are asking, then ask at interview! If she says yes, fine. If she says no then carry on looking or review what you are asking, if you really like her.
But whatever you do, please get it all written down in a contract and make sure you both sign it/