我最终用这个函数代码实现了它。php

// Front end only, don\'t hack on the settings page
if ( ! is_admin() ) {
// Hook in early to modify the menu
// This is before the CSS "selected" classes are calculated
add_filter( \'wp_get_nav_menu_items\', \'display_lasts_ten_posts_for_categories_menu_item\', 10, 3 );
}

// Add the ten last posts of af categroy menu item in a sub menu
function display_lasts_ten_posts_for_categories_menu_item( $items, $menu, $args ) {


$menu_order = count($items); /* Offset menu order */
$child_items = array();

// Loop through the menu items looking category menu object
foreach ( $items as $item ) {

    // Test if menu item is a categroy and has no sub-category
    if ( \'category\' != $item->object || (\'category\' == $item->object && get_category_children($item->object_id)) )
        continue;

    // Query the lasts ten category posts
    $category_ten_last_posts = array(
            \'numberposts\' => 10,
            \'cat\' => $item->object_id,
            \'orderby\' => \'date\',
            \'order\' => \'DESC\'
    );

    foreach ( get_posts( $category_ten_last_posts ) as $post ) {
        // Add sub menu item
        $post->menu_item_parent = $item->ID;
        $post->post_type = \'nav_menu_item\';
        $post->object = \'custom\';
        $post->type = \'custom\';
        $post->menu_order = ++$menu_order;
        $post->title = $post->post_title;
        $post->url = get_permalink( $post->ID );
        /* add children */
        $child_items[]= $post;
    }
}
return array_merge( $items, $child_items );
}

此代码的灵感来源于：http://codeseekah.com/2012/03/05/list-all-posts-in-wordpress-navigation-menu/