Social workers struggled to keep on top of heavy caseloads leaving some vulnerable children at risk due to delays, council directors have confessed.Wigan Council has responded to a "scathing" letter sent by a government watchdog earlier this year, criticising children's services in the borough.Ofsted inspectors said some children remained "at risk or in situations of harm" for longer than they should have due to delays within the department.They identified five areas of improvement for "front