A police watchdog has raised "significant concerns" about the efforts to protect vulnerable children by West Midlands Police.
Her Majesty's Inspectorate of Constabulary (HMIC) said the force needed to take "immediate action" after finding the attitudes of some officers towards victims of child sexual exploitation were "unacceptable".
In a damning report, HMIC assessed 115 cases involving children during an inspection in June and found the responses by the force to nearly half (42%) were "inadequate".
Some sexual abuse cases faced "unnecessary and long delays" and officers blamed "high workloads" for failing to carry out necessary checks, according to the report.
Nine out of 11 cases involving children missing from home were not handled properly, while some officers were "frustrated" by care homes reporting youngsters as missing because they were passing responsibility to police, the watchdog said.
In one child sex exploitation case, information was sent to the force's intelligence unit about men who may have been raping younger girls but no follow-up action took place, HMIC said.
Inspectors found cases where "vital information" had not been recorded including one of children found "living in chaos" because of their parents' criminality and another involving the sexual exploitation of a 13-year-old girl.
They also raised concerns about delays in the arrests of offenders, and found officers had closed cases without sufficient consideration of the risk posed to other potential victims, the report found.
In 13 of 18 assessed cases involving child sexual exploitation, inspectors found "poor risk management of known suspects, significant delays in arrest and a failure to identify suspects", according to the report.
Inspectors also found "indications of a wider network of men offending in groups and gangs" that had not been identified and were therefore not followed up, HMIC said.
The watchdog said only six out of 15 cases of children held in police custody were handled adequately, and some custody staff "lacked awareness and knowledge about child protection".
In one case, a 13-year-old girl in custody told a nurse that she had a history of mental health issues, but this did not trigger a review of her risk assessment, the report found.
The report concluded: "Overall, the force's response to tackling child sexual exploitation has been slow, with inconsistent practice across the force area. There was a general lack of understanding of the extent of exploitation.
"Some of the attitudes officers held towards potential victims of child sexual exploitation or children who ran away were unacceptable and resulted in poor decision making.
"Staff need to understand that children do not make a 'lifestyle choice' to be abused, particularly those who are more vulnerable because of the neglect they have already suffered in their life.
"We recommend that West Midlands Police takes immediate action to review its plans for identifying, disrupting and prosecuting perpetrators involved in child sexual exploitation."
HM Inspector of Constabulary Dru Sharpling added: "The force needs to improve both its approach to the more complex child protection cases and a better understanding of the extent of child sexual exploitation in the West Midlands.
"I would like to encourage West Midlands Police to address our concerns immediately, and have asked that within six weeks it provides us with an action plan to demonstrate how it will act upon these recommendations."
West Midlands Police Assistant Chief Constable Carl Foulkes said: "I want West Midlands Police to be the best in country - dealing with vulnerable children with professionalism and compassion.
"Our Public Protection Unit has been doubled in strength to some 800 officers and staff. That means around 10% of the entire force are engaged in the fight. That displays our level of commitment.
"It's unfortunate that the HMIC inspection came just two days into new arrangements so do not reflect our exciting changes as there was so little time for them to be place.
"We cannot do it alone. We must work hand in hand with our partners, especially the local authorities.
Crime prevention minister Norman Baker said: "I am very concerned by the contents of this HMIC report. The safety of our children, and the elimination of child abuse, are top priorities for this department and the coalition as a whole.
"That is why the Home Secretary has announced an independent inquiry into child sexual abuse within public bodies and non-state institutions.
"She is also leading cross-government work to learn the lessons of past failures and has written to all chief constables stressing the highest standards must be met in tackling child sexual exploitation.
"West Midlands Police must take urgent action to consider all the recommendations in this report and ensure that improvements are made."
Shadow home secretary Yvette Cooper MP said: "Everywhere across the country, not enough is being done to protect children from abuse.
"This HMIC report shows the West Midlands police leadership have made this a priority, but there are still serious problems over the extent of abuse, understanding of the problem and lack of other specialist support.
"And it shows there is a growing problem in the West Midlands and everywhere else about online child abuse which the police are struggling to investigate."