WordPress | Checks to see if a post is a child, that is; does the post have a parent?

is_child.php

<?php
// Check if post has any parents
function is_child($post_id) {
    $post = get_post($post_id);
    $parent = $post->post_parent;
    if( $parent != 0 ) {
        return true;
    } else {
        return false;
    }
}
?>

<?php 
// Example 
if( is_child( $post_id ) ) {
    echo 'I have a parent I am a child';
}
?>