This function (add to functions.php file) creates new logical function to determine if page is parent or child

wordpress_if-parent-or-child.php

<?php
/**
 * Check if Page is a Child of Another Page
 * Gist Keywords: wordpress, parent, child, hierarchy 
 * 
 * @category   WordPress
 * @author     Knol Aust
 * @version    1.0.0
 * @description Function to determine if the current page is a child of a specific parent page.
 */

// Include this function in functions.php

function knolaust_is_tree($pid) {
	global $post;
	if (is_page() && ($post->post_parent == $pid || is_page($pid))) {
		return true;   // The current page is the specified parent or a subpage of it
	} else {
		return false;  // The current page is not related to the specified parent
	}
}

// Include this code in your page template, sidebar, etc.

if (knolaust_is_tree(2)) {
   // Perform actions for pages that are children of page with ID 2
   // You can replace 2 with the ID of the desired parent page
   // Do amazing stuff
}