Thanks for asking.
Adding Facebook pixel code in child theme will require changes in theme files. I suggest you to please download, install and setup child theme from following resource.
After that please add following code in child theme function.php file:
// Begin Facebook Pixel Code
<!-- Replace this line with Pixel Code provided by Facebook -->
add_action( 'wp_head', 'my_facebook_pixel_code' );
// End Facebook Pixel Code
You also have the option to use plugin inrder to get job done. You can use Header and Footer plugin to add Facebook Pixel code.
Here is a tutorial that you can use to get started with Header and Footer plugin.