Children's social care in Hounslow has been found wanting in all areas by Ofsted, in a report published today.
Inspectors found improvement was needed in all three categories in which the council was assessed, including adoption services and the progress made by young people leaving care.
Although they found no major failures, they concluded the authority, which provides care services for nearly 1,800 young people, was not doing enough to protect and support children, young people and families.
The overall judgement was 'requires improvement', the second lowest of four ratings available, which range from 'inadequate' to 'outstanding'.
They criticised the council's social care team for not working closely enough with other agencies to protect children at risk of sexual exploitation and for failing to provide children with access to services to prevent them being taken into care in the first place, among other shortcomings.
"There are no widespread or serious failures that leave children being harmed or at risk of harm. The welfare of children looked after is safeguarded and promoted," the report states.
"However, the authority is not yet delivering good protection and help and care for children, young people and families."
The report outlined a number of changes needed to ensure a better rating, though none were considered to require immediate action.
Among the actions demanded were the introduction of more thorough child protection plans clearly stating what is required from parents and agencies to safeguard children and steps to ensure voluntary care arrangements are 'robustly assessed'.
A council spokesman said the report, which followed an inspection in January, also highlighted a number of good practices. He added that plans were already in place to address the shortcomings identified.
Councillor Lily Bath, cabinet member for children's services at the council, said: "It's reassuring that Ofsted found children and young people are being kept safe - that is the most important job we have.
"They also found no widespread or serious failures in any of our services, which is reassuring under the new tougher regime.
"We know what areas we need to work on to reach the good rating, and already have strong plans in place to address the issues the inspectors have raised. I know that our staff, who work so hard to keep children safe and improve their lives, will rise to that challenge."
One improvement required was a reduction in the time it takes for looked-after children to be adopted, with statistics published last year showing children were waiting up to three years to find a permanent home.
Ms Bath said: "Our adoption service prides itself on finding the right family for each individual child or children, and in the last four years we haven’t had a single adoption breakdown in the borough.
"Sometimes with particular children, especially those with complicated backgrounds of which there are many in Hounslow, this takes longer than we’d like, but it’s vital to get it right.
"The last thing anyone would want is a child being placed with the wrong family only to suffer the heartbreak of this crucial relationship breaking down."
She recognised there was a shortage of local people willing to adopt children and urged more people to get in touch to find out if they could help.
Among the strengths identified in the report were the procedures in place to protect children believed to be at risk of immediate and the support provided to foster carers and their children.
In Hounslow, 1,758 children had been identified as needing a specialist children's service and 305 were being looked after by the council as of March last year, the latest date for which figures are available.
The council's children's social care team was rated 'good' for both safeguarding arrangements and its services for looked-after children when it was last inspected in 2009.
However, this is the first time it has been assessed under the new tougher inspection regime introduced in November last year.
Of the 11 local authorities assessed since then, five have been rated 'good', four have been deemed 'requires improvement' and two have been judged 'inadequate'.
