Child Class
A child class is a class that extends another class. There is no specific keyword related to child classes: unlike parent which is unique and defined, any class that extends a class is its child. A class may have several children.
A child class may be the direct child of a class, or any of the own child.
<?php
// parent class
class Elephpant { }
// child class
class AfricanElephpant extends Elephpant {}
// child class of Elephpant
// child class of AfricanElephpant
class Calf extends AfricanElephpant {}
?>