does the post office and postmen are responsible to police kids' snail mails?

where does this "perfect surveillance" idea come from? i teach my children how to get acquaintances; first in more direct, more supervised way, later let them more and more self-driving. like anything else in parenting, eg. bicycle. but i guess urbanization diminished that skill as well. no need for "perfect surveillance"; no parent wants it. it's not only easier to pass on basic principles, but also makes supervision gradually less neccessary over time.

> parents have in fact full control of snail mail

what? children using e-messaging can just as do snail mails completely on their own (of course they don´t but it's not about going back to analogue world but to form the digital world on the same principles). well, i can imagine in highly urbanized environment, where children are forbidden to go outside, but locked down together with family even making them more isolated, and trusting them "to the phone" to cope with the daily frustration, may easily lead to a situation where phone usage and e-messaging is completely unattended and undisclosed by and with parents, while posting an evelope is at a level of expertise for them. parents ability to be in control of e-messaging is as much as of snail mails.