Found a solution!
$inner_query = new WP_Query(array( 'post_parent' => $parentid, 'post_type' => 'location', 'posts_per_page' => -1 ) );
$countchildren = $inner_query->post_count;
$counterz = 0;
if ( $inner_query->have_posts() ) {
while ( $inner_query->have_posts() ) {
$inner_query->the_post();
$posterid = get_the_ID();
$inner_inner_query = new WP_Query(array( 'post_parent' => $posterid, 'post_type' => 'location', 'posts_per_page' => -1 ) );
$counterz = $counterz += $inner_inner_query->post_count;
};
};