One of the more recent changes is that anyone can now enable a version of this functionality, even if they aren't set up with a child account. (It's under Settings > Messages > Sensitive Content Warning.) In this mode, it behaves similarly to the over-13 mode described above; no one is notified, whether the user chooses to view the image or not.

This mode is probably best understood as "if someone texts me a dick pic, please blur it". I don't think there's any reasonable objection to this.