First of all you must make sure you do a background check on your nanny before you hire him or her. Inform them of your decision to do so and explain to them the importance of why your going to do a background check. Most nannies will not have a problem with this because they will have had experience working with children and know the importance of you having peace of mind. And honestly it really is a law for people to have background checks done if they work in a daycare so it is just as important if they will be in your home and with your family.
Secondly, find out the experience that your nanny for hire has had in the past and ask for references. Make sure that even if the nanny you interviewed is as sweet as apple pie that you call those references. It is professional and adequate for a nanny to provide those things to you. Ask your nanny what kind of education they have had and what they can bring to your child on a daily basis.
And last, have a time where you, your children, and the future nanny can all interact. This does not have to be a long period of time but it is a good opportunity for everyone to meet and get adjusted together. A few ideas for your time to have the nanny meet the children is a walk, dessert and coffee, play time, or even a picnic. Make the transition easier by showing your child this is someone with whom you trust and have confidence in so that when you leave your child will feel secure.