Since the department was last inspected in 2017 its rating has “deteriorated” from good to requiring improvement.
Inspectors carried out their latest full inspection in May and while there are “emerging signs of progress” since other focused visits in the intervening years exposed major problems with workload and management, they say there is still work to be done.
The town hall had said last year its downgrade was anticipated due to a mass exodus of social workers.
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Ofsted found the provision of social work has declined since the last inspection.
The report criticises a reliance on agency staff leading to inconsistency and constant changes in social workers for the children.
Inspectors were more positive about how the service had handled the pandemic and said leadership changes are having an effect.
The report said: "There are sometimes inconsistencies in the application of thresholds between social care and early help, which result in delays in some children and families having their needs fully met.
"The quality of intervention with families in the locality teams is mixed, but with some areas of stronger practice.
“Despite the notable increase in the children in care population in Wigan, the majority of children are settled in foster care, including children living out of the borough.
"There is a lack of appropriate placements for older children and those with more complex needs.”
Ofsted wants improvements in the level of management, support for care leavers and the quality of assessments.
It also acknowledged that although immediate harm is recognised there are delays in discussions due to police availability and domestic abuse concerns are not always robust.
The local authority chose to focus on the positives of the report saying progress is being made and are confident in future plans.
Council director of children’s services Colette Dutton said: “We are pleased that inspectors have emphasised the progress and improvements made in recent years, despite the pandemic and subsequent increased demand for services.
“As the report states; ‘there is a clear focus and determination to make the necessary improvements for children’ and ‘solid foundations…from which improvement activity can be implemented’ are in place.”
“It has also been highlighted that the service has benefitted from significant investment and continues to have ‘strong corporate and political support’.
“We know we have more to do and inspectors recognised that these further improvements are in areas that we are already aware of through our own performance analysis and strong quality assurance processes.
"We are confident that our plans will help us to provide the best services for our children and families.
“It is also really pleasing that Ofsted has acknowledged that social workers are positive about working in Wigan and told inspectors their managers are visible and supportive and they like the culture and the model of practice.
“The challenges facing children’s services across the country are well documented and I would like to take this opportunity to thank all of our workforce who have shown admirable commitment and dedication to working with our most vulnerable children through what has been a really difficult few years through the pandemic.”