Set childpage url without parnt slug

functions.php

<?php
add_action('page_link', 'willy_page_link', 10, 3);
function willy_page_link( $link, $post_id, $sample ) {
    $post = get_post( $post_id );

    if ( 'page' == get_option( 'show_on_front' ) 
      && $post->ID == get_option( 'page_on_front' ) ) {
        $link = home_url('/');
    } else {
        $draft_or_pending = in_array( $post->post_status, array( 'draft', 'pending', 'auto-draft' ) );
        if ( ( isset( $post->post_status ) && ! $draft_or_pending ) || $sample ) {
            $link = user_trailingslashit( home_url( $post->post_name ), 'page' );
        } else {
            $link = home_url( '?page_id=' . $post->ID );
        }
    }
    return $link;
}

add_filter('query_vars','new_vars');
function new_vars($vars){
    $vars[] = 'childpage';
    return $vars;
}

add_filter('rewrite_rules_array', 'wabeo_rewrite_rules');
function wabeo_rewrite_rules( $rules ) {
    $a = array( '([^/]+)/?$' => 'index.php?childpage=$matches[1]');
    $b = array( '.?.+?/([^/]+)(/[0-9]+)/?$' => 'index.php?childpage=$matches[1]&paged=$matches[2]');

    $aRules =  $a + $b + $rules;

    return $aRules;
}

add_filter( 'pre_get_posts', 'willy_find_child_page' );
function willy_find_child_page( $q ) {
	if ( ! is_admin() 
	  && $q->is_main_query() 
	  && isset( $q->query_vars['childpage'] ) ) {

		$q->set( 'name', sanitize_title( $q->query_vars['childpage'] ) );
		$q->set( 'post_type', 'page' );
	}
	return $q;
}