It's a potentially fatal mistake that some parents are still making.

Just weeks ago a Bendigo mum left her six-month-old in the car on a 30 degree day. Her baby had a heart attack and died in hospital that night.

The summer before another mum left her ten-month-old with windows and doors shut tight. Her baby died too.

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Another child, who'd been left strapped in his car seat while his mum went Christmas shopping in the heat of the day, was freed by a good Samaritan. He smashed the 4WD with a hammer and pulled the boy out screaming.

Another mother narrowly escaped jail time after leaving her nineteen-month-old and four-week-old baby in the car - not once but twice on a 40 plus degree day.

Dr Adam West says he treats distressed and dehydrated children rescued from hot cars in the nick of time all too often.

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"There is always the potential for serious and long-lasting injuries to occur," Dr West said.

"We'd commonly see degrees of dehydration in children left in hot environments for long periods of time. If that length of time is excessive it can lead to irreversible brain damage."

Dr West says the results of leaving a child in a hot car can be "agitation, confusion, potentially progressing to coma or even death."

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When a child is left behind in a car that is standing in 35 degree heat, within fifteen minutes of being locked in that child is actually sitting in a whopping 56 degrees.

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Victorian paramedic Paul Holman says it's simply ignorant to leave your child in a car.

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"If you want to damage your children's health, and potentially we could have dead children on our hands, that's the way to do it," Holman said.

If some parents aren't going to apply common sense, the onus may be on us. So when walking through car parks on hot days, keep a look out to see if children or a pet have been left in the back seat. It may be one of us that saves a life.

Veterinarian Dr Alan Bolton has treated two dogs in recent days after they were left in hot cars.

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"Leaving the window down doesn't make very much difference to the temperature with the car at all," Dr Bolton said.

In fact it takes just six minutes for a dog to get into trouble.

"The other thing you need to remember is you may think you are only going to be in the shop for two minutes, but something may happen, so if you get caught up and you are gone for ten minutes, that can be enough to cause damage," Dr Bolton warned.