public void replaceChild(Operator<? extends OperatorDesc> child,
      Operator<? extends OperatorDesc> newChild) {
    int childIndex = childOperators.indexOf(child);
    assert childIndex != -1;
    childOperators.set(childIndex, newChild);
  }
Replace one child with another at the same position. The parent of the
child is not changed

@param child
         the old child
@param newChild
         the new child
ql/src/java/org/apache/hadoop/hive/ql/exec/Operator.java