Communication Safety is a Family Sharing feature that can be
enabled by parents, and it is opt-in rather than activated by
default. When turned on, the Messages app is able to detect nudity
in images that are sent or received by children. If a child
receives or attempts to send a photo with nudity, the image will
be blurred and the child will be warned about the content, told
it’s okay not to view the photo, and offered resources to contact
someone they trust for help.
When Communication Safety was first announced, Apple said that
parents of children under the age of 13 had the option to receive
a notification if the child viewed a nude image in Messages, but
after receiving feedback, Apple has removed this feature. Apple
now says that no notifications are sent to parents.
Apple removed the notification option because it was suggested
that parental notification could pose a risk for a child in a
situation where there is parental violence or abuse. For all
children, including those under the age of 13, Apple will instead
offer guidance on getting help from a trusted adult in a situation
where nude photos are involved.
This seems like a good middle ground to address the above-stated concerns.