Automatic template selector for Wordpress Ancestor/Child Pages

jsp_switch_page_template.php

function jsp_switch_page_template() {
    global $post;

    if (is_page() && !get_page_template_slug( $post->ID )) { //if no template was selected via WP
        $ancestors = $post->ancestors;

        if ($ancestors) {
            $templatePath = TEMPLATEPATH . '/';
            $prefix = 'page-'; //default page template prefix
            $ext = '.php';
            $appender = '_child';
            $parent_id = get_post( end($ancestors) );
            $parent_slug = $parent_id->post_name;

            $page_template = $prefix.$post->post_name.$ext; //default template
            $parent_page_template = $prefix.$parent_slug.$ext; //ancestor template
            $parent_page_child_template = $prefix.$parent_slug.$appender.$ext; //children template

            $template = file_exists($templatePath.$page_template) ? $templatePath.$page_template : file_exists($templatePath.$parent_page_child_template) ? $templatePath.$parent_page_child_template : $templatePath.$parent_page_template;

            if (file_exists($template)) {
                load_template($template);
                exit;
            }
        } else {
            return true;
        }
    }
}
add_action('template_redirect','jsp_switch_page_template');