The firework landed in her 4-year-old son's empty car seat in the rear of the vehicle.
The 26-year-old woman, her son and 2-year-old daughter were all in the front seat as they waited in Union St on Wednesday to pick up the woman's partner from Otago Polytechnic.
They had the windows down because it was hot.
As they waited, a well-kept sporty metallic blue hatchback with chrome wheels drove past and the occupants threw a lit smokebomb firework into her car, the woman said.
"It landed in my 4-year-old's car seat and the car started filling up with purple smoke.
"The kids started crying and were totally freaked out. I had to get them out, but I was freaked out too.
"Something dangerous could easily have happened."
She could not get over the stupidity of the people's actions.
"If he was sitting in that car seat, it would have fallen right in his lap. Why would you do something so stupid? "I think they thought it was a big joke."
She reported the incident to police, who told her they had received other reports of similar incidents, she said.
"I'm big in favour of banning fireworks now. These people need to be stopped. Someone's going to get hurt."
Senior Sergeant Steve Aitken said another person had reported damage to an electronic device after a lit firework was thrown through his car's sunroof in the same area the same day.
There appeared to have been two males inside the offending vehicle.
"This sort of behaviour is unbelievably, absolutely stupid."
Anyone who had any information about the incidents or any similar ones should contact Dunedin police on 471-4800, he said.
