Calls to ChildLine from children in care in the UK have risen by 32% in the past five years, the charity has said.
One in 26 children in local authority care - a total of 3,196 - contacted it in 2009, reporting issues like neglect and sexual and physical abuse, it said.
It is calling for all those in care to have access to an independent advocate to speak up for them.
The Association of Directors of Children's Services was unavailable for comment when contacted by the BBC.
There were more than 83,000 children being looked after by UK local authorities in 2009, including those in foster and residential care, and those in institutions like prisons.
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