Before Luke Whistler’s eldest daughter Abbey, 16, was allowed to have a smartphone, he asked her to sign a contract stipulating how she would use it – in particular, that she promised to put it away by 9 each night.

The Brisbane-based civil engineer and father of four girls has a rule that none of his children can have a smartphone until year 10 – about the age of 15 – to protect them from the perils of social media and devices’ “ability to distract and overcomplicate relationships”.