您可以检查当前类别是否是博客类别的子类别cat_is_ancestor_of() 功能或term_is_ancestor_of(), 或者更好，使用in_category(), 正如您当前所做的，但也要检查子类别。

add_filter( \'single_template\', \'get_custom_cat_template\' ) ;
function get_custom_cat_template( $single_template ) {


    // You want to filter only template for single posts of default post type    
    if( is_singular( \'post\' ) ) {

        $post = get_queried_object();
        // Replace \'3\' with the ID of the \'blog\' category
        $child_blog_categories = get_term_children( \'3\', \'category\' );

        if ( in_category( \'blog\', $post ) || in_category( $child_blog_categories, $post ) ) {

            $single_template = locate_template( \'single-blog.php\' );

        }

    }

    return $single_template;
}