How to create child classes like mysqli class in php -

i building little website, , have problem dealing classes. want create class named message_manager has child named send (like mysqli class has query has child).

i need because want have variables in send class. can me it.

    class message_manager{        var $sender;         var $connection;         function __construct($connection, $sender){          $this -> sender = sender; $this -> connection = $connection;        }     }      class send extends message_manager{       var $message_id;        private function _send($receiver, $message){          //function sends message , generate $id         $this -> message_id = $id;      }       function __construct($receiver, $message){        return $this -> _send($receiver, $message)      }    } 

//sending message

$conn = new mysqli(....); $messenger = new message_manager($conn, $user1); $a = $messenger -> send($user2, $message); $id = $a -> message_id; 

i have tried above code not work. or work-around welcome.