<schema xmlns=“www.ascc.net/xml/schematron” >

<pattern name="a child of selected elements">
     <rule context="CCC">
          <assert test="parent::*[name()='BBB' or name()='DDD']">Element CCC must not be a child of element
               <name path="parent::*"/>
          </assert>
     </rule>
</pattern>

</schema>