The boy died from critical head injuries after the family's white Mazda veered off the road and crashed in bushland north of the Gold Coast on October 25.
A witness saw the car swerve off the road and rushed the mother and injured boy to Beenleigh Police Station.
Officers at the station attempted CPR but the boy couldn't be saved, police said.
The father fled the accident scene and was later found at a nearby address with a one-year-old boy who was uninjured in the crash.
Police will allege the boy's mother was driving the vehicle at the time of the incident.
Both parents have been charged with manslaughter and drug trafficking and are expected to face the Brisbane Magistrates Court on Friday.
Police had earlier alleged the mother and children had travelled from the Gold Coast to collect the father from a Beenleigh address before the crash.
The father was separately charged with domestic violence offences as his emotional family claimed he would never harm his children.
"We are sick of the f***ing lies," the boy's grandfather yelled at the media after the father's appearance at Southport Magistrates Court in October.
"He loves his kids ... he was trying to protect them. He would never hurt them."
A temporary protection order had been in place since June 2024 and the couple were separated, police said.
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