可折叠<；UL><；李>；不起作用

我有一个PHP脚本，它从两个独立的SQL表生成一个ul/li表。但当我试图使用js使它们可折叠时，它根本不起作用。

我做错什么了吗？还是我错过了什么？非常感谢您的帮助。

JScript:

<script type="text/javascript" language="javascript">
$('#usernav').find('ul').slideUp();
$('.child').hide();
$('.parent').click(function() {
   $('#usernav').find('ul').slideUp();
   $(this).find('ul').slideToggle();
});
</script>

PHP:

<?php require_once('/Connections/TDBS_local.php'); 
mysql_select_db($database_TDBS_local, $TDBS_local);
$main_cat="SELECT * FROM main_category";
$main_query = mysql_query($main_cat, $TDBS_local) or die(mysql_error());
$main_result = mysql_fetch_assoc($main_query);
echo("<ul id='usernav'>");
do {
    echo("<li class='parent'>"); 
          $main_link = preg_replace("/[^A-Za-z0-9 ]/", '', $main_result['main_category']); 
          $main_link = strtolower($main_link); 
          $main_link = str_replace (' ','',$main_link);
        echo "<a href='categories/".$main_link."/index.php'>" .($main_result['main_category']). "</a>";
            echo("<ul class='child'>");
    $main_id = ($main_result['id']);
    $sub_cat="SELECT * FROM sub_category WHERE main_category_id = $main_id ";
    $sub_query = mysql_query($sub_cat, $TDBS_local) or die(mysql_error());
    $sub_result = mysql_fetch_assoc($sub_query);
        do {
          $sub_link = preg_replace("/[^A-Za-z0-9 ]/", '', $sub_result['sub_category']); 
          $sub_link = strtolower($sub_link); 
          $sub_link = str_replace (' ','',$sub_link);
                echo("<li><a href='categories/".$main_link."/".$sub_link.".php'>" .$sub_result['sub_category']. "</a></li>");
        } while ($sub_result = mysql_fetch_assoc($sub_query));
            echo(" </ul>
    </li>");
    } while ($main_result = mysql_fetch_assoc($main_query));
    echo("</ul>");
 mysql_free_result($main_query);
 mysql_close($TDBS_local);
?>