WordPress get post with post_child and tax_query of child post?

i need to get the posts with child post of taxonomy, so i have send the following arguments to wp_query but doesn’t return anything, and i didn’t get any error,

$args = array('post_type' => 'event','post_child'=>'location',
                 'tax_query' => array(
                array(
                'taxonomy' => 'kind_of_location',
                'field' => 'slug',
                'terms' => 'restuarant'
                )
                )
                 );
$my_query = new WP_Query($args);

what is the problem here? and how can i get the posts related with my child post’s taxonomy’s?