The following is basic working DropDown menu, childís appear on hover parent text.

HTML Code:
<script type="text/javascript">
  $(document).ready(function () { 
    $('#nav ul').hide();

    $('#nav li > a').hover(
      function () {$('ul', this.parentNode).stop().slideDown(100);}
    );

   $('#nav li').hover(null, 
      function (e) {$('ul', this.parentNode).stop().slideUp(100);}
   );

  }
  );
</script>

<ul id="nav">
  <li><a href="#">Parent A</a>
    <ul>
      <li><a href="#">Sub a1</a>
          <ul>
            <li><a href="#">Item a1.1</a></li>
            <li><a href="#">Item a1.2</a></li>
            <li><a href="#">Item a1.3</a></li>
        </ul> 
      </li>
      <li><a href="#">Sub a2</a></li>
      <li><a href="#">Sub a3</a></li>
    </ul>
  </li>
  <li><a href="#">Parent B</a>
    <ul>
      <li><a href="#">Sub b1</a></li>
      <li><a href="#">Sub b2</a></li>
      <li><a href="#">Sub b3</a></li>
    </ul> 
  </li>
</ul>
Iíve added above a third level under submenu, but it's not opening and closing this level.

Iím not sure in this case if I need to change the html code or is it only the JavaScript that needs to be changed so that the script will work properly also with the added 3rd level.