Gursewak Dhillon, 23, told police he did not seek medical help because police would find out and it might take him ''too far from my dreams'' to live in Australia, court documents reveal.

Three-year-old Gurshan was alive when Dhillon placed him unconscious in his car boot and drove around for three hours, before dumping the young child in grass by the roadside on March 4, some 20km from his family's home in Lalor.

The boy's lifeless body was found by a truck driver about 6.30pm that day.

Indian national and part-time taxi driver Dhillon pleaded guilty in Melbourne Magistrates' Court yesterday to manslaughter by criminal negligence.

Dhillon, who lived with Gurshan and his parents, admitted to police that he knocked the toddler unconscious with the front screen door.

''I think he was running towards the door to come in. I didn't even see him. I just heard the noise,'' he said.

Dhillon said the boy fell to the ground and wasn't moving.

But he didn't want to tell the boy's mother, who was in the shower, because the police would find out and he thought it might affect his residency.

''I was afraid,'' he said.

He placed Gurshan in the boot of his car, thinking he should take him to hospital.

Instead, he drove around in a panic before dumping him, not knowing if he was still alive.

Forensic tests showed that the temperature in the boot could reach 47 degrees in the afternoon sun.

Dhillon's wife Simarjeet Kaur initially denied knowledge of his involvement to protect him.

But she later told police she saw him holding the unconscious toddler near the front door.

She admitted getting his car keys and watching Dhillon take the toddler away in the car.

''We talked about what to do. He said he would take him to the doctor.''

After dumping the boy, Dhillon returned home about 3.30pm, and joined his housemates in searching for Gurshan.

Dhillon, who came to Australia with his wife in 2008 on a bridging visa, was charged three days after Gurshan's body was found.

He is being investigated for offences relating to his previous entry into Australia on a passport with a different name.

He is in custody awaiting a Victorian Supreme Court directions hearing on September 21.