People responsible for children caught throwing stones at cars from motorway bridges could be prosecuted.
Police in Gloucestershire are telling parents in the county to keep an eye on their children to make sure they do not throw things at cars - or they could be taken to court.
The warning comes after two youths threw a stone from a bridge onto a busy road in Cirencester, sending it smashing into a van passing below.
No-one was injured in the incident on the A429 Bristol Road on Monday, but the driver, a 56-year-old Gloucester man, was left shocked when the four-inch square rock crashed through his windscreen.
Officers say someone could be seriously hurt if the dangerous prank is repeated.
They say parents have a responsibility to control their children during the summer holidays.
And they are making it clear that those who do not could face the consequences of their children's actions.