Programmatically get all work item children

Hi all,
I would programmatically find all children of work item and, after, analyze the custom attribute of these.

I try in this way:

IWorkItemReferences referencesCopy = wis.resolveWorkItemReferences(wiCopy, null);	

List<IReference> links = referencesCopy.getReferences(WorkItemEndPoints.CHILD_WORK_ITEMS);

for (IReference lin : links) {						

	List<IAttributeHandle> childsWorkItem = ((IWorkItem)lin.getLink().getWorkingCopy()).getCustomAttributes();

	for ( IAttributeHandle iah : childsWorkItem) {

		IAttribute customAttribute = (IAttribute) (repositoryItemService.fetchItem(iah, null));

		if (customAttribute.getIdentifier().equalsIgnoreCase("defectalreadyopened")) 

		{



			.....



		}

	}

}								

but I obtain this error:

java.lang.ClassCastException: com.ibm.team.links.internal.links.impl.AuditableLinkImpl incompatible with com.ibm.team.workitem.common.model.IWorkItem

Any suggestions?

Thanks
Andrea