Police will investigate whether a toddler was properly restrained after the child was found in the footwell of a wrecked car.
A car was T-boned in Roxburgh Park at about 8pm on Thursday, with the two-year-old found critically injured in the car's footwell, police say.
The toddler suffered head injuries and was taken in a critical condition to the Royal Children's Hospital.
His condition has since been downgraded to serious, a hospital spokeswoman told AAP on Friday.
Attending police officer Sergeant Dean Pickering said the child was found in the footwell of the car.
"Initially we didn't even know there was a child in the car, literally because the child had been thrown around," he told the Nine Network.
Police believe the child was not properly restrained.
"It's incredibly dangerous, our most precious cargo need to be buckled up," Assistant Commissioner Doug Fryer told the Ten Network on Friday.
The car was likely hit when it pulled out into oncoming traffic, police say.
The driver, 30, was trapped for 30 minutes before being taken to the Royal Melbourne Hospital with back and abdominal injuries.
The 20-year-old driver of the other car, Ali Kadik, said he was overwhelmed when he found out a child was in the car.
"I got a bit emotional when I found out there was a kid in there because the last thing I need to know is I've taken a little kid's life," he told reporters on Friday.
The investigation continues.
