get the child object in a WTDocument via webject

Hi Guys,

How can we do to get the child object in a WTDocument via webject?

<%@page language="java"%>
<%@taglib uri="http://www.ptc.com/infoengine/taglib/core" prefix="ie"%>
<%String wcAdapter = com.infoengine.au.NamingService.getVMName();%>
<ie:webject name="Query-Objects" type="OBJ">
 <ie:param name="INSTANCE" data="<%=wcAdapter%>"/>
 <ie:param name="TYPE" data="wt.doc.WTDocument"/>
 <ie:param name="GROUP_OUT" data="resultQuery"/>
 <ie:param name="OBJECT_REF" data="$(@FORM[0]obid[0])"/>
 <ie:param name="ATTRIBUTE" data="number"/>
</ie:webject>
<% 
 final String strDirection="usedBy";
%>
<ie:webject name="Query-Links" type="OBJ">
 <ie:param name="INSTANCE" data="<%=wcAdapter%>"/>
 <ie:param name="GROUP_OUT" data="resultLink"/>
 <ie:param name="DIRECTION" data="<%=strDirection%>"/>
 <ie:param name="OBJECT_REF" data="${resultQuery[0]obid[0]}"/>
 <ie:param name="ATTRIBUTE" data="*"/>
 <ie:param name="TYPE" data="wt.doc.WTDocumentUsageLink"/>
</ie:webject>
<ie:webject name="Return-Groups" type="GRP">
 <ie:param name="GROUP_IN" data="*"/>
</ie:webject>

Thanks.