The three-year-old’s body was discovered by the driver on Tuesday inside a Goodstart Early Learning minibus parked outside Hambledon State School in Cairns.
He was picked up from his family’s home at 9.30am and found by the same driver at 3.15pm.
Exactly what happened during that time is unclear, but the boy was not reported as missing.
“It’s early days in the investigation at this stage, and I can’t say where it will go,” Detective Inspector Jason Smith said on Wednesday.
A police investigation is focusing on the movements of the bus and if the boy was inside the entire time from when he was collected to when he was found. The driver had other appointments during the day.
The distraught man was admitted to Cairns Base Hospital for shock and investigators are yet to interview him.
Police are combing through CCTV footage captured across the city as part of their investigation, and the bus itself is one of the crime scenes.
Goodstart boss Julia Davidson, who flew to Cairns late on Tuesday, says the group’s staff are devastated and shocked by the death.
“I want to extend our deepest condolences to the family who have suffered such a tragic loss,” she said in a statement.
“We will of course offer them all possible assistance.” The centre at Edmonton is closed and bus services will be temporarily suspended from Wednesday.
“This was not an easy decision to make as this service enables many vulnerable children to access early learning, however we need to ensure our safety processes and procedures are the best they can be,” Ms Davidson added.
“Our bus services will complete their scheduled pick up and drop off services today, with additional checks in place until all children are home this afternoon.” Counselling is being provided to staff and their families, while Mission Australia has offered chaplaincy support.
Detectives from the Child Protection Investigation Unit are investigating and a report will be prepared for the coroner.