What are common pitfalls when accessing variables from parent classes in PHP and how can they be avoided?

Common pitfalls when accessing variables from parent classes in PHP include not using the correct visibility (public, protected, private) for the variable in the parent class, not using the correct scope resolution operator (:: or ->) when accessing the variable in the child class, and not properly initializing the parent class before accessing its variables in the child class. These pitfalls can be avoided by ensuring that the variable in the parent class is declared with the appropriate visibility, using the correct scope resolution operator to access the variable in the child class, and calling the parent class constructor before accessing its variables in the child class.

class ParentClass {
    protected $variable = 'Hello from parent';

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

class ChildClass extends ParentClass {
    public function __construct() {
        parent::__construct();
        echo $this->variable;
    }
}

$child = new ChildClass();