The past two weeks I have been doing a unit on "Cybersafety" with my 6th grade advisory class. We just did a lesson on this very kind of thing.
I emphasized to them that once it's out there on the internet, it's out of their control, and, likewise, sending on cellular phones.
By their responses, you can actually identify the kids who have been given guidance and had limits set, vs. those who are given no guidance regarding the use of the Internet as well as cell phones.