The number of children in care contacting ChildLine has risen by almost a third in five years, the charity said.
One in 26 of these "looked after" children contact the service about failings in the care system, a ChildLine report revealed.
Director of ChildLine Peter Liver said: "Most children in care are well looked after by dedicated carers and professionals.
"But a minority continue to be failed by the care system. When this happens, children need to know there is someone there to speak up for them who is independent from the local authority."
There were over 83,000 children in foster, residential or other forms of care in 2009.
In all, 3,196 looked after children - some as young as five - contacted ChildLine over 2009-10 with problems about being in care. Many were suffering physical and sexual abuse and neglect and felt lost and helpless in the care system.
The report calls on local authorities to make sure fostered and other looked after children always have an adult to speak up for them when they need help.
Mr Liver added: "Every day, looked after children talk to us about lives filled with pain and hurt. After the trauma they've been through, children need a special quality of care - at least as good as a good parent can offer.
"Instead, we hear from children who have been beaten or sexually assaulted while in care. Others feel abandoned in care or unloved by their new carers. Some are intimidated by other children. Many have reached crisis point.
"ChildLine highlighted the plight of these children in a report published 16 years ago and some of the same issues persist. These failings go back at least a generation."
