If you don’t need to use loops, this will work for you.
<?php
$our_services = get_field('our_services'); // 'our_services' is your parent group
$service_one = $our_services['service_one']; // 'service_one' is your child group
?>
<?php echo $service_one['service_heading']; // 'service_heading' is a subfield of your child group ?>