As I take this scenario, a major disaster occurs, without warning, that requires evacuation (earthquake, dam break, volcanic eruption, toxic release, etc.) . Schools, day care centers and other car-givers are (should be?) responsible for moving their charges to shelter. Parents are also directed to shelter.
This is why everyone in the family needs to know/carry the phone numbers and/or e-mail addresses of at least two relatives or friends that live in geographically dispersed regions. In case of an emergency where the family is seperated, everybody checks in with them. (Communication within the affected area may not be possible.) They then act to coordinate family reunification. Since they are out of the affected area, they can also be the info clearing house for other relatives/friends. This should be part of everybody's disaster plans.
JimJr