Update: 截至年月日WordPress 3.7 （2013年10月），添加了CSS类以指示主题菜单中的子菜单项和页面-无需使用自定义walker，因为它在WordPress core中得到了处理。

CSS类被命名为menu-item-has-children 和page_item_has_children.

在主题模板中输出导航：

wp_nav_menu( array(
    \'theme_location\' => \'navigation-primary\',
    \'container\' => false,
    \'container_class\' => \'\',
    \'container_id\' => \'\',
    \'menu_class\' => \'\',
    \'menu_id\' => \'\',
    \'walker\' => new Selective_Walker(),
    \'depth\' => 2
    )
);

class Selective_Walker extends Walker_Nav_Menu {
    function display_element( $element, &$children_elements, $max_depth, $depth=0, $args, &$output ) {
        $id_field = $this->db_fields[\'id\'];

        if ( is_object( $args[0] ) ) {
            $args[0]->has_children = !empty( $children_elements[$element->$id_field] );
        }

        return parent::display_element( $element, $children_elements, $max_depth, $depth, $args, $output );
    }

    function start_el( &$output, $item, $depth, $args ) {
        if ( $args->has_children ) {
            $item->classes[] = \'has_children\';
        }

        parent::start_el(&$output, $item, $depth, $args);
    }
}

<ul>
    <li><a href="#">Home</a></li>
    <li class="has_children"><a href="#">About</a>
        <ul class="sub-menu">
            <li><a href="#">Our Mission</a></li>
        </ul>
    </li>
    <li><a href="#">Services</a></li>
    <li class="has_children"><a href="#">Products</a>
        <ul class="sub-menu">
            <li><a href="#">Lorem Ipsum</a></li>
            <li><a href="#">Lorem Ipsum</a></li>                
        </ul>
    </li>
    <li><a href="#">Contact Us</a></li>
</ul>

享受

这个函数正是您想要的。它还向您展示了一种修改导航菜单项的非常有效的方法。此外，您还可以通过项目过滤器打开它以获得更高级（如子主题）的功能：

/**
 * Classes for a navigation named "Topnav" in the nav location "top".
 * Shows examples on how to modify the current nav menu item
 * 
 * @param (object) $items
 * @param (object) $menu
 * @param (object) $args
 */
function wpse16818_nav_menu_items( $items, $menu, $args )
{
    # >>>> start editing

    // examples for possible targets
    $target[\'name\'] = \'Topnav\';
    // The targeted menu item/s
    $target[\'items\'] = array( (int) 6 );

    # <<<< stop editing

    // filter for child themes: "config_nav_menu_topnav"
    $target = apply_filters( \'config_nav_menu_\'.strtolower( $target[\'name\'] ), $target );

    // Abort if we\'re not with the named menu
    if ( $menu->name !== $target[\'name\'] ) 
        return;

    foreach ( $items as $item )
    {
        // Check what $item contains
        echo \'<pre>\'; print_r($item); echo \'</pre>\';

        // First real world example:
        $item->classes = \'span-4\';

        // Second real world example:
        // Append this class if we are in one of the targeted items
        if ( in_array( (int) $item->menu_order, $target[\'items\'] ) )
            $item->classes .= \' last\';
    }

    return $items;
}
add_filter( \'wp_get_nav_menu_items\', \'wpse16818_nav_menu_items\', 10, 3 );

如果你想做下拉列表，你可以只使用css。在WP中自定义导航，WordPress会自动分配类。子菜单至子菜单ul。尝试此CSS

    nav li {position:relative;}
   .sub-menu {display:none; position:absolute; width:300px;}
    nav ul li:hover ul {display:block;}

if ( $this->has_children ) {
    $item_output .= \'has_children\';
}