Giving a child any device with an Internet connection requires oversight. A sudden wave of adolescent emotion could generate a photo or a social media message that could become what Gail Lovely, a former teacher and owner of Lovely Learning, a consulting firm for schools, refers to as a "digital tattoo" that comes up in a job interview 10 years later.

The knowledge that messages will vanish also frees users from what Cornell Professor Jeff Hancock calls the "digital tattoo." "If you do something online, it's difficult to remove," he said.

Yet the dispute underscores an issue that is becoming more prominent as a growing number of digital devices use a plethora of identification numbers to communicate with each other effectively and securely.

"My problem is that it happens without the user knowing," said Bruce Schneier, an encryption expert and industry consultant. "It's the slow erosion of privacy on the Net without informed consent."

Jason Catlett, president of Junkbusters, a consumer privacy organization, called the ID numbers a "digital tattoo."