Parents are still leaving children in cars despite temperatures in the 30s, Ambulance Victoria says.
Paramedics have been called to 111 cases already this year, including seven yesterday.
"It appears most of the calls were because of deliberate acts where parents made a decision to leave a child in a car while they go into a shop," Ambulance Victoria spokesman Paul Bentley told AAP.
"Sadly we've had a couple of children die in recent years and it's just not worth the risk."
None of the children yesterday required treatment, he said.
Tests by Ambulance Victoria show on a 29C day the temperature inside a car can reach 44C within 10 minutes, and 60C in 20 minutes.
"Even if you're going to duck into the shop for just a couple of minutes there's a chance you might get delayed and that puts your child in danger," Mr Bentley said.