re order custom query by meta_value

i’m using “types plugin” creating child related posts with the main ones.
and trying now to re-order these posts according to ‘meta_value’ but it does nothing!

here is my code:

<?php
    $child_posts = types_child_posts('features', array('order' => 'DESC', 'meta_key' => 'order', 'orderby' => 'meta_value meta_value_num', 'suppress_filters' => true )) ;
    foreach ($child_posts as $child_post) {
		echo $child_post->fields['order'];
		echo '<h4>'.$child_post->post_title.'</h4>';
     }?>

'order' or 'wpcf-order'
not working and cause a blank page!

any ideas ?

thanks