Residential care costs could blow out to $7b a year

Queensland has the largest number of vulnerable children in residential care in Australia. (Dan Peled/AAP PHOTOS)

Residential care housing a state's most vulnerable children could cost taxpayers more than $7 billion as the number of kids requiring placement surges.

The Queensland Family and Child Commission has modelled that at current rates where the number of kids in residential care has grown by 85 per cent over five years, the cost will also balloon.