Adavnced custom fields, ACF

Własny filtr na custom query w acf

function childpages_query( $args, $field, $post_ID )
{
    $args['post_parent'] = $post_ID;

    return $args;
}

add_filter('acf/fields/relationship/query/name=pages_childpages', 'childpages_query', 10, 3);