Enable Zooming in Child Theme

Hi How can I enable zooming in my child theme? To enable it you put the code <meta name="viewport" content="width=device-width, initial-scale=1" /> and you put it in your header.php. I won't to add it to a plugin or the functions.php. I tried this.

function zoom_site() {
		 echo '<meta name="viewport" content="width=device-width, initial-scale=1" />';
}
add_action('wp_head', 'zoom_site', 1);

But it didn't work. Any suggestions would be much appreciated. Thanks