The expert group, which was set up last year by the Department of Health and Department for Education to improve mental health support for children in care, said those working closely with looked-after children, including foster carers, children's home staff and special guardians, often lack training to support their often complex mental health needs.
A report by the group, published today, calls for all those working with looked-after children to receive specific children and young people's mental health training "so they are equipped with the appropriate skills" to support them.
This should have a particular focus on managing behavior and be consistent across sectors, so that all professionals and carers are adopting the same approach, the report adds.
"A whole system framework of training that prepares and supports carers and professionals, respecting their roles in supporting young people, is crucial," the report states.
"This collaborative approach would both provide those at the frontline of supporting our young people with the resources to respond to and contain a range of behaviours and mental health needs, and ensure that everyone involved in their care is coming from the same understanding and knowledge base.
"There was a consistent request from stakeholders to have training that focused on how to manage behaviours and individual wellbeing."
The expert group singles out the Fostering Changes Programme, which offers mental health training to foster carers and has been developed at the Maudsley Hospital, South London in conjunction with King's College London, as an example of good practice.
"The approach seeks to train foster carers to maintain children and placements, address behavioural challenges and also to skill them up to thinking about how to collaborate and engage with young people about their mental health wellbeing and concerns," the report states.
Proposals by the group for all councils to be required to appoint virtual mental health leads, as reported by CYP Now last month, have also been confirmed.
The report states that leads should be responsible for ensuring all looked-after children and care leavers are getting support for their emotional wellbeing and mental health.
The group also wants every school to have a designated teacher with training in identifying and understanding the mental health needs of all their pupils who are in care.
Other recommendations include ensuring all carers receive support for their own mental health and emotional wellbeing.
There is also a call for ministers at the DoH and DfE to work together to ensure that all looked-after children and care leavers have access to mental health support.
The expert working group has been co-chaired by Peter Fonagy and Dame Christine Lenehan, with support from the Social Care Institute for Excellence (Scie).
Scie also spoke with 100 children and young people and 100 adult practitioners as part of the work
Tony Hunter, chief executive of Scie, said: "The mental health of adults and children has been an increasingly high-profile issue in recent times.
"Yet the mental wellbeing of looked-after children hasn't always had the same focus. So our recommendations today are timely, especially as co-productive approaches have been used to fully involve young people in drawing up highly relevant and considered ways forward.
"Let's hope the report and its recommendations will go a long way to improving the wellbeing and mental health of looked-after children and young people."
A study published by Barnardo's in September found that two thirds of care leavers with mental health problems are not receiving specialist support.