You should be able to do this fairly easily with the save_post hook. When one of the child pages is saved your hook will fire and allow you to firstly check the post type, and then if the post is indeed a child of your main post, where you want to update the URL, version etc.
You can retrieve the child post values using ACF get_field:
$latest_version = get_field('software_version', $post->ID);
Then update your parent using the ACF update_field:
update_field('current_version', $latest_version, $post->post_parent);
Un-tested, but that gives you the basics.