Hi
Don’t copy theme-functions.php file to the child theme, because it’s not a template file.
You can just create a new functions.php file in the child theme folder, write your own function to override the van_posted_on() function as below.
/*Post meta info*/
if( !function_exists( 'child_posted_on') ){
function child_posted_on(){
?>
<span class="blog-article-info"><?php printf(__('By %s','OldCar'),get_the_author());?> / <?php printf( __( 'in %2$s', 'OldCar' ), 'entry-utility-prep entry-utility-prep-cat-links', get_the_category_list( ', ' ) ); ?> / <?php the_time(get_option('date_format'));?></span>
<?php
}
}
Then, copy posts-normal.php and posts-grid.php file to the child theme folder, edit these file, replace van_posted_on() to child_posted_on()
Thanks