That doesn't mean it is on the books.

It could be just a cautionary measure to prevent a subsequent lawsuit from a parent, or an abduction investigation or charge (which can happen on the road as an officer sees too few adults travelling with far too many kids to be a single family).

Though there may be also a chance there is a law for private transport, such as family vans, which does not apply to cabs. Though I am also pretty sure it does apply to mass transport like buses or trains, which (Trucker probably has stories) does influence the decisions runaways have to take.