WordPress: is a child page

is_child.php

/**
*   Child page conditional
*   @ Accept's page ID, page slug or page title as parameters
*/
function is_child( $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 ) ) {
        return true;
    } elseif ( in_array( (string) $parent_obj['post_title'], $parent_array ) ) {
        return true;    
    } elseif ( in_array( (string) $parent_obj['post_name'], $parent_array ) ) {
        return true;
    } else {
        return false;
    }
}