How singleton passing property to child

Place.php

<?php
class Place 
{
  /**
   * @var string
   */
  private $key;
  
  /**
   * @var PlaceNearby
   */ 
  private $nearby
  
  public function __construct($key) 
  {
    $this->key = $key;
    $this->nearby = new PlaceNearby();
  }
}

PlaceNearby.php

<?php
Class PlaceNearby 
{
  public function __construct() 
  {
    // do something here
  }
  
  public function execute()
  {
    // How can i get my parent key (@_@)
    $this->parent->key;
  }
}