The problem with that is, parents be like:
>Here kid, take my key, go get me some beer.
Everyone everywhere gets forced to deal with bullshit, then the people it is supposed to be protecting circumvent it directly.
The same can happen with any type of authentication, unless you are ok with someone pointing a webcam and authenticating you non stop.
When I was 8 or 9, my Father would often give me 50p to go down to the nearby pub to get him 20 cigarettes and a half-pound bar of chocolate, which came to 48p. Always "and where's my change then?" when I returned. Tight git.