Final answer:
The correct message key for a missing child feared to be in danger is Code Adam, an alert used to locate and ensure the child's safety by monitoring exits and searching the premises.
Step-by-step explanation:
When a child has been reported missing and the child's life is feared to be in danger, the correct message key to be used for the entry of this child is Code Adam. A Code Adam is an alert which is typically announced, often in public areas like shopping malls, hospitals, and other facilities, when a child has gone missing. It is a procedure to help locate the child rapidly and ensure their safety. A Code Adam involves steps such as a detailed description of the child being broadcast, monitoring of all exits, and a thorough search of the premises.