Lancashire Police said children aged "around 11" dropped "a large piece of ice" onto a car on Padiham's Dryden Street at about 20:10 GMT on Saturday.
The next day at about 15:15, four boys "aged about 12 or 13" dropped ice on a car near junction 10 of the M65.
The drivers were "shaken" but not injured, a spokesman said. Police are now seeking those responsible.
Sgt Michael Burnett said it "may have been kids who thought they were simply playing a practical joke, but both incidents could have been so much worse".
He added: "These incidents have put peoples' lives in danger and caused serious damage to their vehicles.
"The drivers are lucky to have escaped unharmed."
The lives of motorists were put at risk when children dropped ice from bridges, smashing two cars' windscreens.