Police Search For New Witness After Children Die In Hot Car

Police are appealing for help to track down a man who possibly witnessed the alleged murder of two Queensland toddlers.

The two girls --Darcey-Helen, two, and Chloe-Ann, one -- died on Saturday after being left in a car at Waterford West, with the temperature reaching 31 degrees when they were found.

Kerri-Ann Conley, 27, the mother of the pair has been charged with their murders.

She is the first person to be charged under the new definition of murder, which includes "reckless indifference to human life".

Police want to speak with a man who was in the area during the time the girls were in the car.

CCTV footage shows a man seen wearing a high-visibility shirt, tradesman shorts, work boots, a white hat and carrying a black backpack.

He appears to be Caucasian and was walking along Logan Reserve Road, towards Muchow Road, around 1.15pm on Saturday, police said.

If anyone saw this man, they are urged to contact police.