code: public int getNumChildren(final Graph graph, final Node subject) {
          LOGGER.trace("Getting number of children: s:{}, g:{}", subject, graph);
          return (int) asStream(listObjects(graph, subject, CONTAINS.asNode())).count();
      }
docs: Get the number of child resources associated with the arg 'subject' as specified by the triple found in the arg
  'graph' with the predicate RdfLexicon.HAS_CHILD_COUNT.
  
  @param graph   of triples
  @param subject for which child resources is sought
  @return number of child resources