As Sydney families grapple with massive mortgages, the rising cost of living and fears of job insecurity, grandparents are increasingly taking the financial burden and dipping into their life savings to pay their grandchildren's schools fees.

Almost one-third of grandparents are planning to draw down on their superannuation to pay school fees, research by industry super fund Rest shows.

Baby boomers are stepping in to help as their offspring feel the pinch, with official figures revealing that NSW residents are taking out bigger mortgages, borrowing on average $78,100 more than a year ago, with the average new loan for an owner-occupier now $437,100.

Families are also relying on double incomes, with recent census data showing that in 23 per cent of families in Sydney both parents work full-time.