Delays examining computers are also undermining West Mercia Police child protection investigations.
But HM Inspectorate of Constabulary (HMIC) praised the force for improving the way it investigates child sexual exploitation cases.
West Mercia Police said it was "pleased" its work had been recognised but accepted it had more to do.
"As HMIC report, we have implemented many improvements since the initial inspection, however there are areas highlighted in the review where we need to continue to improve and we will strive to meet these standards, Supt Kevin Purcell said.
The force has said it will also be introducing an extra 54 officers and staff to deal with child abuse as well as domestic abuse within the West Mercia and Warwickshire force areas.
The inspection, last August, is part of ongoing child protection investigation checks on all police forces in England and Wales.
HMIC spokeswoman Wendy Williams said there had been some "clear improvements" since its initial inspection, including bringing in more staff and clearing a large backlog of work.
"As child protection is such an important area to get right, there are still areas where we would like to see the force improve," she added.
"It needs to improve the time it takes to examine computer and electronic devices, as the current delays undermine ongoing investigations. It also needs to improve how it works with partner agencies, to provide a coherent service to children at risk."
HMIC will continue to monitor how the force performs, she said.
A police force is still unnecessarily detaining children in custody, an inspection has found.