Closing time at the library

We have been having problems with kids being left outside of the library after closing time. Apparently, their parents arrive later at the library to pick them up OR the parents display complete irresponsibility and think the library will babysit their kids for them. In an effort to assuage this problem, we have been telling kids to make an arrangement for a ride home at one hour before close. Kids being alone outside the library building after close is a problem for us and we hope this proactive approach might help. (We hate calling the police on parents who think the library provides a babysitter service).