Untitled

How can I can get a child class's attributes into the parent class's methods
<?php
require_once("user.php");
$user = new User();

$user->auth("Scott", "rascal");
echo $user->username;
?>
<html>
<head>
    <title>test</title>
</head>
<body>

</body>
</html>

Notice: Undefined property: Database::$dbFields in /Users/scottmcpherson/Sites/phpsites/projectx/application/models/db.php on line 24

Warning: Invalid argument supplied for foreach() in /Users/scottmcpherson/Sites/phpsites/projectx/application/models/db.php on line 24

Notice: Undefined property: Database::$tableName in /Users/scottmcpherson/Sites/phpsites/projectx/application/models/db.php on line 83

Notice: Undefined property: Database::$id in /Users/scottmcpherson/Sites/phpsites/projectx/application/models/db.php on line 85

Notice: Undefined property: Database::$dbFields in /Users/scottmcpherson/Sites/phpsites/projectx/application/models/db.php on line 24

Warning: Invalid argument supplied for foreach() in /Users/scottmcpherson/Sites/phpsites/projectx/application/models/db.php on line 24

<?php
require_once("db.php");

class User extends Database{

    public $dbFields = array('username', 'password');

    public $tableName = "users";
    public $id;
    public $username;
    public $password;

    public function auth($user, $pass){
        $this->username = $user;
        $this->password = $pass;

    }
}
?>

class Database{


 public $db;

public function __construct() {
    $this->connect();
}

public function connect(){
try {
    $this->db = new PDO("mysql:host=".DB_SERVER."; dbname=".DB_NAME, DB_USER, DB_PASS);
    $this->db->setAttribute( PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION );
    } catch (PDOException $e) {
    echo 'Connection failed: ' . $e->getMessage();
    }
}

public function properties() {
    $properties = array();
    foreach ($this->dbFields as $field) {
        if (isset($this->field) || property_exists($this, $field)) {
            $properties[$field] = $this->$field;
        }
    }
    return $properties;
}