Sort hierarchical Custom Taxonomy

I have a hierarchical custom taxonomy named children and inside the taxonomy i have two children “easton” and “kiari” the code calls all posts from the taxonomy, but they are still sorted independently so i get all posts sorted by post date for easton, and then all posts sorted by post date for kiari. The question is how do i combine the taxonomy and sort by post date so i get posts sorted by date regardless of weather its from easton, or kiari.

Current sort example:
easton july 30 2011
easton july 15 2011
easton july 1 2011
kiari july 30 2011
kiari july 14 2011
kiari july 2 2011

Desired Sort Example
easton july 30 2011
kiari july 29 2011
easton july 15 2011
kiari july 14 2011
kiari july 2 2011
easton july 1 2011

here’s my code:

<?php

// List posts by the terms for a custom taxonomy of any post type
$tax = 'children';
$tax_terms = get_terms( $tax );
if ($tax_terms) {
	foreach ($tax_terms  as $tax_term) {
	$args = array(

		"$tax" => $tax_term->slug,
		'post_type' => 'post',
		'post_status' => 'publish',
		'posts_per_page' => -1,
		'caller_get_posts'=> 1,
    	'orderby' => 'post_date',
    	'order' => 'DESC',

	);

		$my_query = null;
		$my_query = new WP_Query($args);

		if( $my_query->have_posts() ) : ?>