If you need your nanny to be available during 'on-call' hours, then it makes sense that she is compensated at her regular rate of pay for 'on-call' hours (because you have control over her time). The law requires that you compensate your household employee for each and every hour she works for you (ie: when you control her time).
In this case, your nanny may agree to be available to come 'on-duty' as needed. Since you do not completely control her activities during those 'on-call' hours, but you retain the ability to have her work on short notice, it makes sense to compensate her at a reduced rate of pay while 'on-call' and pay her regular rate of pay for the time she is called in ('on-duty') to work. For example, picking up an ill-child from school and returning to your home.
If you do not want to pay anyone for hours when you *may* need child care and you have the flexibility to cover that time yourself (or have access to other care providers), then there is no need to compensate your nanny for time she is not working and may not be available to work. However, you must be prepared for the likely circumstance when your nanny will not be available when you need her. Be sure to have a back-up plan in place!
...but she is free to do as she pleases during the 'On-Call' time?
As you can see, there are pros-and cons to each of the three distinctly different situations described above. Once you determine your needs, it will be easy to negotiate a compensation plan with your nanny that makes sense for everyone.
________________________________________________
Additional Resources:
Would you like more information?
YES, PLEASE!