Nearly half of looked after children in Wakefield have a diagnosed mental health problem, a new study has revealed.
Figures show that 45 per cent of youngsters in the care of Wakefield Council have a known mental health condition, compared to around 10 per cent of all children in the district.
Looked after children are also much more likely to have a physical health problem and issues such as speech or language impediments, according to a report prepared for Wakefield's corporate parenting committee.
Sam Turner, from the children in care charity Become, said that mental health conditions often arise as a result of traumatic experiences in early life, which are being "compounded" by problems within the care system.
He also said that the numbers of those with a problem in Wakefield reflected a nationwide trend.
"Sadly that is a picture we recognise," Mr Turner said.
"Often children into come into care because they've experienced abuse or neglect. They may also have had a bereavement or a disability.
"Then the process of moving into care itself causes a lot of upheaval, potentially.
"Often it's the impact of the pre-care experience which causes the mental health problem in the first place.
"But we find that the assessments used by the care system are inconsistent, and so those mental health issues can go unnoticed.
"That can compound some of those experiences they've had in their early years.
"Often these children suffer a lot of instability and have to frequently move placements and move schools. That's an experience a lot of their peers won't have had themselves."
More than 500 children are currently in the care system in Wakefield.
The local authority said that mental health assessments carried out by social workers, revealed that results from 50 per cent of the children were a "cause for concern" or "borderline" healthy, suggests that some youngsters have undiagnosed conditions.
Mr Turner said that "brutal" cuts to services by central government was at the root of problems in the system.
He added: "Even when mental health needs are identified, access to Children and Adolescent Mental Health Services (CAMHS) is very poor.
"Lots of children are being denied treatment.
"Stability is one of the key things that can improve a child's mental health in the long-term.
"Those who are with a family for a long time will report better outcomes. Ultimately it's about listening to the wishes of the child, and making sure they're in the right place."