Meeting Places
Plan for things to go wrong in your plans. Since it's difficult to account for every possibility that might ever arise, make plans for everyone to meet up in specific places if specific criteria is met. In the previous example of children in school for example, you might plan for everyone to head towards the school of your youngest child in the event that there are no specific plans of action for an event that happens, or if the event causes more destruction than you had originally planned for.
If a surprise flood occurs while everyone is away from home and it washes away your neighborhood, you won't be able to follow an original plan that said to meet back up at the house. For this type of event you need a fallback meeting place, or Plan B, defined with a specific alternate meeting place for everyone to head for.