Aside from the parental obligation, there's also legal obligations entailed with parents' supervision of their children as stated in some laws in Australia.
Emma Aldersea, a criminal lawyer from Slater and Gordon, specify these laws and why should be cautious in leaving their children home alone.
Laws relating to leaving children unattended in each Australian state and territory
(as at 20 March 2017; Source: Slater and Gordon)

Source: As filed by Slater and Gordon