Young adults who don't leave the family home are collectively costing their parents an extra £1.2 billion a year, a report estimates.
Parents with grown-up children who are still living at home spend an extra £456 on them a year compared with "empty nesters", according to the Centre for the Modern Family think-tank, which has been set up by pensions provider Scottish Widows.
The research found that as well as shouldering the cost of their child's basic bed and board, parents are also forking out for services used by their adult children such as Netflix, as well as for their mobile phone bills, holidays, haircuts, clothing and even beauty treatments.
The study found those with children over 18 who are still living under their roof are spending £122 a month typically on their grown-up children, compared with £84 a month for their empty nest counterparts - adding up to an annual difference of £456 a year.
If the findings were projected across the UK, this would mean parents with a "full nest" of adult children are spending £1.2 billion more on their offspring compared to parents whose children have flown the nest.
Anita Frew, chairwoman of the Centre for the Modern Family said: "While it is heartening to see that the UK's families are so willing to support one another, we are in danger of nurturing a Peter Pan generation of children who are reliant on their parents well into adulthood for all types of spending - which could have a major impact on parents' finances for later life."