Leading child advocacy services say a NSW government report into the social services sector has exposed a misguided funding model that has seen billions of dollars spent on the wrong services.

The Forecasting Future Outcomes report, released by the Berejiklian government on Friday, found seven per cent of people aged under 25 will account for half of the estimated $100 billion cost of social services by the time they are 40 years old.

Young families are among vulnerable groups not receiving adequate funding, according to a report. Credit:Gabriele Charotte

Julie Hourigan-Ruse, chief executive of Fams, the peak body for child advocacy in NSW, said the extensive data revealed what many in the sector had long suspected.

"It speaks to, for the first time, that government has been investing in the wrong stuff," Ms Hourigan-Ruse said.