More foster carers are urgently needed as the care system in the UK struggles to meet the needs of the most vulnerable children, a charity warns.
The Fostering Network says care services have seen a rise in demand for foster homes following the death of Baby Peter in London in August 2007.
The network says there is a shortage of more than 10,000 foster families.
The charity is urging ministers to make investment in foster care services a priority, despite pressure on budgets.
In its report - Bursting at the seams - the Fostering Network said the care system had seen an "unprecedented rise" in the number of children needing foster placements since the death of Baby Peter came to public attention.
In total, 53,934 children in the UK needed a foster home in 2009, compared with 51,009 in 2007.
The report said increased demand meant many foster carers were being asked to look after children outside their area of expertise, and for whom they might not have the right skills.
It said new foster carers were often being asked to take in children with more challenging behaviour than in the past, not allowing carers to build up their confidence and skills.
There was also a marked rise in demand for homes for under-fours which had led to a shortage of homes for teenagers as younger children were prioritised.
Similar concerns were voiced in a report published by NSPCC, the Children's Society and York University last month.
The Fostering Network urged the government to make sure funding for local authorities took account of the increased numbers of children coming into care.
It said fostering services must ensure pay and allowances for foster carers was sufficient to recruit and retain enough people with the right skills and experience.
As part of its research, the Fostering Network conducted interviews with 76 fostering services across England, Scotland and Wales and questioned over 300 foster carers.
Report author Helen Clarke said the system was under "unprecedented pressure".
"The impact of the rise in children needing foster homes and the shortage of foster carers means the system is no longer sustainable and budget cuts could be devastating.
"Investment in foster care must remain a priority for both central and local government.
"There needs to be a renewed sense of urgency to recruit more foster carers and to ensure the current foster care workforce is properly paid and supported. Otherwise, our society's most vulnerable children will suffer."
Chief executive of the Local Government Association John Ransford said the system was never designed to deal with the increase in numbers experienced in the past two years.
"The work foster carers do looking after children in the care system is invaluable," he said.
"Councils are well aware of their duty to help and advise foster families, who deserve the gratitude, respect and support of everyone."