Are you going to query both two child post types 'indon-stat'and 'myanmar-stat'?
Please try modify it like this:
...
$args = array('meta_key'=>'_wpcf_belongs_updatelist_id', 'meta_value' => $update_list_post[0]->ID,'post_type' => array('indon-stat','myanmar-stat'));
...
http://codex.wordpress.org/Class_Reference/WP_Query#Type_Parameters