Victorian children in state care were involved in more than 1000 sexual incidents in the past year, including more than 100 rapes.
The shocking figures were the worst for children in residential care, who make up five per cent of children in care but account for 62 per cent of category one incidents.
A damning 2015 report into Victoria's residential care system found it "creates opportunities for the sexual abuse of children".
The government accepted the report's recommendations, and the Commissioner for Children and Young People's 2015/16 annual report says some programs are working.
"However, reports relating to incidents of sexual exploitation of children and young people living in residential care continue to rise, indicating the need for urgent action on all of the inquiry's recommendations," the report said.
There were 1019 sexual incidents involving children in state care in 2015/16, making up one third of all category one incidents.
They included 138 rapes, 200 indecent sexual assaults, and 412 "sexual exploitation" incidents, up from 162 the year before.
"The increase is the result of enhanced knowledge and awareness amongst those working with young people at risk," says the report, released on Thursday.
The Department of Health and Human Services annual report also revealed 20.7 per cent of child protection cases were unallocated as of June 2016.
"With youth crime at record rates, these vulnerable children need to be protected from abusive behaviour," opposition children's spokeswoman Georgie Crozier said.
Families and Children Minister Jenny Mikakos said the government was taking steps to improve the safety of children in care through its Roadmap for Reform policy.
"(The) policy is shifting the children and family services system from crisis response to prevention and early intervention," she said.
Victoria's child protection system has strengthened its relationship with police to increase reporting and early intervention in cases of sexual exploitation.
More than 330 new child protection workers have been hired since May 2015 and spot audits of residential care facilities have started.
