Whether a post is a child of a parent

isChild.php

<?php

/**
 * Whether a post is a child of a parent
 *
 * @param mixed $parent Page ID, slug or title
 *
 * @return boolean
 * @access public
 */
function isChild($parent = '')
{
    global $post;

    $parent_obj = get_page($post->post_parent, ARRAY_A);
    $parent = (string) $parent;
    $parent_array = (array) $parent;

    if (in_array((string) $parent_obj['ID'], $parent_array)
        || in_array((string) $parent_obj['post_title'], $parent_array)
        || in_array((string) $parent_obj['post_name'], $parent_array)
    ) {
        return true;
    }

    return false;
}

/* <> */