JavaScript - Traversing the HTML DOM using childNodes causes errors in Non IE browsers

Question

I have the following table being rendered in my browser. It's generated from the server side.

<table id="tblQuestions" class="tblQuestionsContainer" border="0">
 <tr>
  <td id="1" class="tdQuestion">Are u an indian citizen ?</td>
 </tr><tr>
  <td><table id="answer-1" border="0">
   <tr>
    <td><input id="answer-1_0" type="radio" name="answer-1" value="1" /><label for="answer-1_0">Yes</label></td><td><input id="answer-1_1" type="radio" name="answer-1" value="0" /><label for="answer-1_1">No</label></td>
   </tr>
  </table></td>
 </tr><tr>
  <td id="2" class="tdQuestion">Do you have a passport ?</td>
 </tr><tr>
  <td><table id="answer-2" border="0">
   <tr>
    <td><input id="answer-2_0" type="radio" name="answer-2" value="1" /><label for="answer-2_0">Yes</label></td><td><input id="answer-2_1" type="radio" name="answer-2" value="0" /><label for="answer-2_1">No</label></td>
   </tr>
  </table></td>
 </tr>
</table>

Now I am using the following code in my JavaScript to validate the radio button's checked state.

 var tblQuestionBoard=document.getElementById("tblQuestions");
  tblAnswer = tblQuestionBoard.rows[1].childNodes[0].childNodes[0]

Now tblAnswer should be an object having the Table with id "answer-1"

In IE, I am getting it. But in Mozilla and rest of the browsers I am getting it as undefined.

How to solve this?