Child Records are associated with a parent and one of the situations it is used is where a large task needs to be broken up into smaller dependent tasks and often owned by different people or teams. The parent task can only complete its work flow (and move to the end state) when all dependent tasks are completed (and in their end states).
An example is where an incident is raised for an application not being accessible and the application team investigates and finds it is due to a problem of the server on which the application is running. They will then raise a child incident and route it to the server team. Once the child incident is resolved, the application team can verify that the application is up and running and resolve the parent incident.
Anther application of this feature is in Enterprise Service Management where a business process has a number of sub-processes which need to be completed for the parent process to complete. An example is the employee onboarding process. A typical employee onboarding process involves multiple sub-processes owned by various functions like assignment of a seat owned by Admin, enabling access and providing an ID which is owned by Security, allocation of a computing resource owned by IT, setting up the payroll entry owned by Finance etc. Each of these processes have their own workflow. In such a case HR creates a parent record and child records can be created for the sub-processes. At any time HR will have a view of the status of each of the sub-processes and can track them to completion. The parent record can be closed (moved to the end state) only if all child records are moved to the end state.
Refer to the topic Service Desk->Settings->General Settings->Child Record Configuration for configuring this feature.
On click of the child record submit button, 
a new record screen is displayed. If the project is an incident management
project, an incident submit screen is displayed.
Based on the configuration settings for child records, the field values can be pre-populated from the parent record. Once the fields are updated, click on 'Submit' to create the child record
The following configuration settings can be done for child records
Fixed fields in child records, which have to be populated from the parent record
Roles which have access to the child record
Additional fields configuration in the child record (Refer the topic on Additional fields in Service Desk->Settings->Fields & Forms->Additional Fields.)
The child record format including the prefix for the number and end states in the workflow for the child record.
The child records get displayed along with the parent records in the list views. However while setting the filter for list views, you can choose to view only Parent or Child records or both.
