While a prospective nanny may have excellent credentials and references, it's incredibly important that she or he "clicks" with you and your family.
Although you'll have uncovered a lot of specific information about your nanny candidates during the screening process, interviews give you and the nanny the chance to talk face-to-face. During the interview, introduce the candidate to your children and observe how they interact. Describe your expectations and be clear about duties, hours, wages, vacation time and listen to how the candidate responds.
Also keep in mind that nannies aren't required to have any specialized training, licensing or degrees, but if it's important to you and your family, add it to your criteria. Highly qualified nannies will not only be certified in first aid and CPR training (a must) but will also have taken courses in child development. The International Nanny Association offers a nanny credential exam. Ask about the candidate's education and training.
And in the end, don't forget to trust your instincts.