也许你必须用这个

$categories=get_categories(
    array( \'parent\' => $cat->cat_ID )
);

foreach ($categories as $c) {
    var_dump($c);
    // what you really want instead of var_dump is something to
    // to create markup-- list items maybe, For example...
    echo \'<li>\'.$c->cat_name.\'</li>\';
}