Open a child case type in Case Designer.
Caution: Ensure that you open the correct version of your case type if it has multiple parent case types. The instantiation details for a child case type are unique to each parent case type.
On the Settings tab, click Instantiation.
Select the Manual instantiation check box.
Optional: In the Allow only when field, press the Down Arrow key and select the name of a when condition that controls when the option to create a child case is displayed in the Add Work menu of a parent case.
Alternatively, you can enter a unique name and click the Open icon 
to create a new when condition.
Click Save.