public static void makeChild(
    Operator<? extends OperatorDesc> ret,
    Operator<? extends OperatorDesc>... oplist) {
    if (oplist.length == 0) {
      return;
    }

    ArrayList<Operator<? extends OperatorDesc>> clist =
      new ArrayList<Operator<? extends OperatorDesc>>();
    for (Operator<? extends OperatorDesc> op : oplist) {
      clist.add(op);
    }
    ret.setChildOperators(clist);

    // Add this parent to the children
    for (Operator<? extends OperatorDesc> op : oplist) {
      List<Operator<? extends OperatorDesc>> parents = op.getParentOperators();
      parents.add(ret);
      op.setParentOperators(parents);
    }
  }
Returns an operator given the conf and a list of children operators.
ql/src/java/org/apache/hadoop/hive/ql/exec/OperatorFactory.java