A Perth mother says she and her young son were lucky to escape injury after a water-filled balloon thrown from a Leederville overpass smashed through her windscreen.

Police say Taryn Bourne’s car was one of three vehicles damaged on May 17 by the balloon attacks.

She had just left a children’s playdate at Galup, formerly Lake Monger, and was driving with her three-year-old son when the balloon shattered her windscreen.

It happened near the intersection of Vincent Street and Lake Monger Drive.

“It was such a shock,” Ms Bourne said.

“I basically took off from the traffic lights and then suddenly my windscreen was smashed.”

The mother said she had only been travelling about 40km/h when the impact shattered the glass.

“I would have only been doing about 40km because I’d just taken off from a traffic light,” Ms Bourne said.

Photos of the aftermath show the balloon shot was a bullsye, smashing the centre of the windscreen. Part of the offending balloon remained stuck in the glass.

Her son was sitting in the back seat.

“He was just like, ‘What was that?’ He was a bit shocked,” Ms Bourne said.

The woman believes the outcome could have been catastrophic had the balloon struck a motorcyclist or caused a driver to lose control from the impact.

“If someone was going faster or if it was a motorbike or a P-plater or an elderly driver, it definitely could have been a lot worse,” she said.

“Like if there was a lot of traffic, I could have swerved or something.

“It definitely could have ended up with us getting hurt or even worse.”

Ms Bourne said the balloon was no ordinary water bomb, saying it was a regular balloon filled with water and “about the size of a soccer ball.”

Several motorists stopped to help after witnessing the frightening incident, while a City of Vincent worker reportedly captured footage of a group of young people on the bridge and passed it on to police.

The City of Vincent would not provide the video.

About 40 minutes after Ms Bourke’s incident, she said she saw the group again carrying more balloons.

“They were on e-bikes and e-scooters and they had motorbike helmets on,” she said.

The mother initially thought the group were teenagers but later believed some may have been much younger after her husband got a bit closer.

“I initially thought they would have been about 15,” she said.

“My husband said some of the kids looked quite small. So they could have been as young as like nine or ten.”

What shocked her most was that the group allegedly returned despite police already attending the area.

“There were police in the area and the kids still came back again,” she said.

“They would have seen that they’d smashed my window and then just did it again.”

On a Leederville community Facebook group, another victim came forward after their car was damaged in the exact same on the same day, about 4pm.

Ms Bourne commented saying her incident had occurred about an hour before and she had witnessed the group return to the area, again, armed with another water balloon.

Wembley Police are continuing to investigate the incident which they believe occurred between 2.50pm and 3.10pm.

“About 3pm, police received multiple reports that a group of unknown youths had dropped water balloons onto vehicles travelling along Vincent Street, from a bicycle overpass adjoining the Mitchell Freeway, in Leederville,” WA Police said.

Police confirmed that as a result of the incident three vehicles sustained significant damage, including smashed windscreens.

“Police attended and conducted patrols, however, the group had fled prior to arrival,” they said.

“The unknown group is described as being aged between approximately 14 and 17 years, some travelling on e-scooters and bikes.

“The group were last seen fleeing north bound along the cycle path towards Richmond Street in Leederville at about 3:20pm.”

Police warned that throwing objects at moving vehicles is extremely dangerous and can cause serious crashes, injury or death.

“Throwing objects at vehicles may constitute a range of offences under Western Australian law depending on the circumstances, including criminal damage, acts causing risk of bodily harm, assault offences, and offences involving intent to endanger life, all of which carry significant penalties including imprisonment,” they said.

Officers are appealing for anyone with information relating to the incident, including CCTV, dash-cam, or mobile phone vision, to report to Crime Stoppers or by calling 1800 333 000.