The Cope family: Steve and Lee with their sons Dylan (left) and Brock. Credit:John Veage "It's a case of younger people staying at home longer," said bureau demographer Andrew Howe. Steve and Leanne Cope, from Cronulla, have two sons in their 20s living in the family home as well as two teenage sons. "It's beautiful chaos here," Mr Cope said. "We love it." Mr Cope said his adult sons, Brock and Dylan, who are both tradesmen, are saving to buy one or two investment properties.

"They can then use that to buy something in an area where they want to live in future," he said. "They're more than welcome to stay at home but they've got to have a focus on saving." Mr Cope, who owns a pest control company, said it would be impossible for his adult children to afford separate local accommodation. "I guess there's a chance we're going to eventually have four adult children living in the house with us," he said. Traditionally, the largest group to move suburbs each year in NSW have been those in the 20- to 24-year-old age group. But that peak has shifted to the 25- to 29-year-old age group since 2009.

New regional internal migration figures published by the bureau also reveals a larger number in the 30- to 34-year-old age group are moving house that in the past, a trend consistent with young adults living longer at home. University of NSW Professor Lyn Craig said these trends suggest the transition to independent adulthood has become more difficult in Australia. "It seems to be related to the cost of housing and the cost of supporting yourself," she said. "People are marrying later and having children later so the whole transition to adulthood is being delayed by a combination of factors."

"It's not like these households with young adult children are turning into share houses where everyone mucks in," she said. "The division of labour is very similar to what you would expect from households with younger children." Professor Craig said the trend for young people to remain at home for longer has far-reaching social implications and threatens to exacerbate social inequalities. "As family support for children goes on for longer, it's harder for people who have fewer resources," she said.

The high cost of housing is one factor driving this trend but there are other causes. Young adults are spending more time at university to prepare for new knowledge-intensive jobs and staying at home while they do it. Living with parents can also free up funds for travel and other lifestyle choices. Bethany Hudson, a 24-year-old IT worker who lives with her parents in Peakhurst, said her main motivation for living at home was to save money to start a business. "For me, living at home is more of a liberating choice because it means I will be able to do what I really want to do, quicker," she said. Steve Cope said the Cronulla lifestyle was a major reason his adult sons wanted to stay at home.

"The 23-year-old lives in a granny flat with a pool at his front door and all the freedom in the world," he said. "All of us surf so it's a fantastic lifestyle - we're very blessed where we live. "The older boys would probably have to move away into a regional centre to have the same coastal lifestyle without huge expense." Mr Cope said he has several neighbours and friends with "multiple adult children at home". The number of 20-somethings moving suburb has declined in all states and territories since the middle of last decade.

There was a 20 per cent fall in Victorians aged 20-24 moving suburb between 2008-09 and 2013-14. Improved regional internal migration estimates introduced by the bureau earlier this year has allowed more detailed analysis of where people move each and at what age. These estimates draw on Medicare data as well as the national census.