A nanny doesn't necessarily live with the family, but the 'primary care setting' (i.e. where they take care of the children most of the time) is the child's home. They can also be part-time.

The key difference is that a nanny is usually a formal salaried employee with regular contracted hours, whereas a babysitter is typically paid an hourly rate and is self-employed.

https://www.care.com/a/what-is-the-difference-between-a-baby...