As he had done every night for the past 60 years, Eric Johnson sipped a glass of milk on Friday evening and took in the view from his balcony in Oyster Bay in Sydney's south.

Just after 10.30pm, a white van pulled up in front of his house.

Inside, by the dim yellow cabin light, Mr Johnson, 88, saw two young girls left alone as the male driver wandered off down the street.

Concerned that the girls had been left unattended, the former shipwright went down to inspect the van.