The family of a 10-year-old-boy who died after being locked in a car boot at Mooroopna, north of Melbourne, on Sunday has described his death as a "tragic end to a game of hide-and-seek".

In an online fundraising campaign, Bentley's aunty, Lainey Sutton, said his family and friends were utterly devastated.

"December 15th will forever be the day that we pause for a moment to remember our inquisitive, car-loving, Minecraft enthusiastic, neurodiverse 10-year-old Bentley," the post read.

"In a tragic end to a game of hide-and-seek, our world stopped.

The post went on to reveal another family member, Bentley's grandmother, died a fortnight ago.

"As you could understand, the heartache and costs of dealing with the loss of one family member is numbing, let alone losing a second in such a short time frame," Ms Sutton said. 

"We understand that this time of the year can be financially and emotionally difficult for anyone. It is with heavy hearts that we ask for financial support to help us give our precious Bentley the send off he deserves."

Ambulance Victoria said paramedics responded to the incident in Mooroopna at 3:20pm on Sunday.

The temperature reached 35 degrees Celsius in the Goulburn Valley town that afternoon.

A police spokesperson said the boy's death was not being treated as suspicious and that the circumstances surrounding the death were still being established.

Police will prepare a report for the coroner.

Greater Shepparton City Council Mayor Shane Sali said Sunday's events were "devastating".

 "As a parent of young children, my thoughts are with the family at this extremely devastating time," he said.