[Psycho_Bunny]

how does one enforce this?

Quite simply.  Just off the top of my head, pull over drivers in the lane whose sole passenger is a child, or when a car in the lane is pulled over for speeding ask for the drivers license of the passenger.

[HEY4QDEMS]

when a car in the lane is pulled over for speeding ask for the drivers license of the passenger.

That's a frightening position.