The two pupils had waited on the bus as the pram was freed, but then got off.
The bus then started to roll backwards.
Michaela said the driver stood and watched the bus, with about 10 passengers inside, roll away "collect two cars, spin around and smash into a ute".
"It was ridiculous ... it was lucky there were no cars coming when the bus spun around."
The bus scraped the side of two cars, a Toyota Platz and Honda Odyssey, parked behind the bus stop.
The bus travelled across South Rd and crashed backwards into a double-cab Ford Courier utility.
The owner of the utility, a staff member at pet shop Mudpuppy, who did not want to be named, said she was working when she heard a "huge crash".
"It sounded like a rubbish truck being emptied."
Bus passenger Madeleine Broadstock said the back wheels of the pram had been caught under the bus but the pram was released before the bus rolled backwards.
The runaway bus felt like it could have rolled, she said.
"We were scared, we were panicking."
Ritchies Coachlines Ltd regional manager Malcolm Budd said the driver had failed to engage the handbrake.
The bus was well-maintained and was issued a certificate of fitness on Thursday, Mr Budd said.
St John spokesman Ian Henderson said an ambulance was deployed but no-one was injured.
A police spokeswoman said police were investigating the cause of the crash.
The findings would determine if further action was taken, she said.
A police spokesman said it was not clear if there was infant in the pram at the time of the incident or whether it had been in danger.
Both lanes on a section of South Rd were blocked for about an hour.
