Set Post Private if no linked Post Objects (ACF)

I have created 2 custom post types (using CPT UI). Parent and children. Many children can be associated to one parent using a post object field(add_to_parent).

I would like the parent post type to be automatically set to private if there are no post objects (children) linked to it, and then once a child is associated to the parent, the parent then becomes published.

Any ideas would be greatfully received.