I think looking for a "personal police" is missing the point.

When I was a child, and "misbehaved" ... [[[ do we even agree children do??  If not ... well, happily I'm too old to ever have to live around your children ]]] ... when he would scold me, often he would say "I don't like being the policeman"

His point was until I (as a growing child) developed my own sense of what is right/wrong, he would happily provide that guidance for me -- which, as a parent, is his obligation/prerogative/joy.

As is being done - exploding this Child Supervision thread into the perennial "Nanny State" argument does have one merit.  If an individual fails to adhere to guidelines of their Society, they are punished.  That is what Society is for.  The Nanny State advocates would like to see members of Society be given greater guidance by the State so as to avoid those excursions of acceptability.  The detractors believe everyone has the same intuited/divinely inspired ability to adhere to Society's laws on their own.  Both miss the others point, as has been done in this thread.  That is, all people up to a certain age must have guidance and after a certain age; must have the chance not to have that guidance.  With an appropriate period of transition.

Quick question for those claiming "let the child alone, she'll be happier on the Internet without muddling parents."  ... do you have dependents?  you taught to drive?  by giving them the car keys and then going on vacation?  and now they have perfect driving habits?  Which they miraculously learned on their own: no doubt YouTubing Mario Andretti, and reading that one wikihow page.