In WHENCHANGED rule, use System.RelatedLinkCount, for example,
<FieldDefinition refname="DCS.CI.ChildrenResolved" name="Children Resolved" type="String">
<DEFAULT from="value" value="False" />
<COPY from="value" value="False" />
When the initial work item is created the fields contains "False". I then change the value to "True". Then I add a child task and the value does not change to "False" although the value of System.RelatedLinkCount did change.
The WHENCHANGED rule is not working with System.RelatedLinkCount in TFS 2010 and TFS 2012. However, this rule can work with System.AttachedFileCount.
Related thread link: http://social.msdn.microsoft.com/Forums/en-US/tfsadmin/thread/05f63fa5-325b-4a81-9e83-95c399cd9bcd
Thanks and Best Regards,