Your children are the most important people in this situation. They must be included. Talk to them about the nanny before her arrival. Discuss their feelings. If a nanny is leaving, talk to them about your feelings and ask them to share theirs.
Children are very sensitive to the feelings of the family and know when changes occur.
Once the nanny arrives, even when you have made all the appropriate preparations, there will be a period of adjustment. Establish A Good Beginning. It will take some time for a nanny to become acclimated. She is coming at a difficult time. Another nanny has just left and is missed by the family.