One easy way to handle this is to create a page which includes the
childrens using #includeTopic("pagename")

You could add the following script at the end of your parent page

#if($context.action=="pdf")
#set($sql = "where doc.parent='$doc.fullName'")
#foreach($item in $xwiki.searchDocuments($sql))
#includeTopic($item)
#end
#end

Ludovic