Enqueue CSS & JS with unique version numbers

functions.php

add_action( 'wp_enqueue_scripts', 'theme_enqueue_styles' );

function theme_enqueue_styles() {
	// Grab CSS and JS urls.
	$theme_styles  = "/css/child-theme.css";
	$theme_scripts = "/js/child-theme.js";

	// Use filetime() as the version number - so each time you rebuild the CSS or JS, you get a new version number to bust the browser cache
  // Note: we use the local path with filetime(), not a url
	$css_vers = filemtime( get_stylesheet_directory() . $theme_styles );
	$js_vers = filemtime(  get_stylesheet_directory() . $theme_scripts );

  // Enqueue the CSS and JS with the version number parameter 
	wp_enqueue_style( 'child-styles', get_stylesheet_directory_uri() . $theme_styles, array(), $css_vers );
	wp_enqueue_script( 'child-scripts', get_stylesheet_directory_uri() . $theme_scripts, array(), $js_vers, true );
}