The state department responsible for out-of-home care last year moved to a team case management model as a result of staffing shortages.
It meant some young people no longer had individual safety officers but were instead managed by a team who they could contact via a generic email or telephone number.
Almost 400 children were shifted to the model in the first four months of its operation.
Some of the cohort had complex needs, such as a disability, being in care for less than 12 months or being in youth detention.
Tasmania's Commissioner for Children and Young People Leanne McLean said the model failed to uphold the rights of young people as required under legislation.
She said some children did not find out about the change until after it began and the model didn't comply with their rights in several areas, including to feel safe and have regular case worker meetings.
Ms McLean said the model's intention was to ensure at-risk cohorts kept a dedicated safety officer and "stable" children would be supported by a team.
"Inconsistent with the plan ... young people who required more than low-intensity case work (who were not stable in their placement) were allocated to team-based case management," she said in a report published on Wednesday.
Ms McLean said some children had not been visited regularly by safety officers.
She said some young people told her they no longer knew who their guardian was or didn't know where to go for help.
The model said visits would be made by other appropriate services, but Ms McLean said there was no evidence of this occurring.
Ms McLean said safety officers found it challenging to meet the needs of children allocated to teams.
"Officers assigned to work on the teams were required to respond to requests about children and young people that they did not know," she said.
"This created chaotic environments in which there was little time for proactive work.
"Instead, as one (safety officer) put it, their work was 'putting out spot fires'."
An inquiry examining child sexual abuse in Tasmania's institutions, which published its final report in September, found out-of-home care needed urgent funding.
Ms McLean said child protection services in the state were chronically under-resourced.
Minister for Education, Children and Youth Roger Jaensch said Ms McLean's report detailed issues the government was working on.
"Aspects of the model (were) brought about as a matter of necessity when we had very low staffing numbers," he told reporters.
"We needed to ensure the staff that we had where they were best and most needed. We make no apologies for that.
"We will work towards a longer-term model that meets everyone's needs and objectives."
Mr Jaensch said the government was working to recruit more staff.
