CSS <div> issue.

Suppose I have the following setup

<div id=“leftColumn”>
  <div id=“leftChild1”><?php require(“include/errorMsg.inc”) ?></div>
  <div id=“leftChild2”><?php require(“ads/googleAd1.inc”) ?></div>
</div>

<div id=“rightColumn”>
  <div id=“rightChild1”><?php require(“include/article1.inc”) ?></div>
  <div id=“rightChild2”><?php require(“include/article2.inc”) ?></div>
</div>

<div id=“centerColumn”>
  <?php
    if ($mode=“a” {
      require(“include/form_a”);}
   else {
      require(“include/form_b);}
   ?>
</div>

Now suppose that leftChild1 is an error display module and is only to be inserted if there is an error detected in the code that is building the main content by the php code form_a or form_b.

Since the form code in the centerColumn is beyond the leftChild1 element, is there a way to define the leftColumn container early and then later insert the children divs into it depending upon the need?