Failing at adding child theme functions

Hi,

Just got a child theme sorted which has the following functions.php file:

<?php
add_action( 'wp_enqueue_scripts', 'theme_enqueue_styles' );
function theme_enqueue_styles() {
    wp_enqueue_style( 'parent-style', get_template_directory_uri() . '/style.css' );

}

?>

I want to add the following function to this file (it works out how many units of a product are still available);

**/Product Stock Quantity Check For Course Calendar Page/**

add_shortcode('product_stock', 'product_stock');
  function product_stock( $atts ) {
    if ( ! $atts['id'] ) {
      return '';
    }
    $product = get_product($atts['id']);
    return (int) $product->stock;
  }

How do I add this to the functions.php file??

I’ve tried this (below) and it just breaks the site.

<?php
add_action( 'wp_enqueue_scripts', 'theme_enqueue_styles' );
function theme_enqueue_styles() {
    wp_enqueue_style( 'parent-style', get_template_directory_uri() . '/style.css' );

}

**/Product Stock Quantity Check For Course Calendar Page/**

add_shortcode('product_stock', 'product_stock');
  function product_stock( $atts ) {
    if ( ! $atts['id'] ) {
      return '';
    }
    $product = get_product($atts['id']);
    return (int) $product->stock;
  } 

?>

Anyone know what I should be doing here?

Thanks!!