Would the nanny be working full time, 5 days per week or would they work part time? This may make a difference to some questions you ask, such as you may want to know what they do on the days they do not work for you which may restrict your ability in future to change days.
Find out about their experience and training:
How long have you been a nanny and what ages of children have you cared for?
What other childcare work have you done, be it paid or unpaid?
What have you found challenging?
What childcare training and qualifications do you have?
Think of situations that may occur:
What would a typical day look like, give the ages of my children?
Have you ever had to take a child to Urgent Care, A&E, Doctors?
How do you deal with a child having a tantrum?
If you had to fill your car with fuel while caring for my children, would you take them with you when you go to pay?
Tell me what you would do if baby is asleep in their car seat and it was time to collect from school/nursery.
If I told a child they were not allowed something and they then asked you, what would you do?
Decide if you will have the interview with your children present or not. You can always arrange a second interview for your best two candidates to see how they interact with your children.
Think about how payment will work:
We are offering x gross per year - are you happy with that salary?
We will pay you monthly and part of that may come via Childcare Voucher which may arrive a few days in to the following month - are you used to being paid in that way?
We will be using Childcare Vouchers / Tax Free Childcare scheme to help with childcare cost, do you meet the criteria and will register or are you already registered?
Make sure you understand about Net and Gross pay. Some nannies will still talk in terms of Net (what they get after taxes) pay. You will find more information about Net vs Gross pay on here and from nanny payroll companies such as Nannypaye.