Only a third of police cases involving vulnerable children are handled to a good standard, inspectors have found.
Of the 576 cases involving vulnerable children across eight forces in England and Wales looked at by HM Inspectorate of Constabulary (HMIC), 177 were found to have been dealt with to a good standard, while 220 were viewed as inadequate and 179 were deemed as adequate.
The cases, which the HMIC examined as part of the National Child Protection Inspection programme, are part of a system which displays inconsistency and weakness from the first contact of a child with police and through to the investigation.
The findings are from three reports launched by the HMIC, which warns that the police must reassess their approach to child protection or risk failing a new generation.
Dru Sharpling, who led the inspections, said: "Children must come first - there can be no compromise when it comes to child protection. Getting it right most of the time can never be the explanation for failures that have devastating consequences for the child, carers and families."
She noted that the quality of risk assessments - the fundamental building blocks of child protection practice - is patchy.
On "too many occasions" the HMIC found that investigations into child abuse or neglect were poor and plagued by delay. They also found that responses to reports of offences against children - ranging from online grooming to domestic abuse - was inadequate.
It was noted that in one case police and social services agreed, without consulting a medical practitioner, that the likely cause of vaginal bleeding in a four- year-old was eczema even though the child had made sexual allegations against a family member.
In contrast, the report highlighted a detective, with much-needed good communication skills, helped a 13 year-old who was having a sexual relationship with a 20 year-old.
The detective identified the girl as a victim of sexual abuse, arranged for specially trained officers to interview the family, provided advice and reassurance, quickly involved child care services, arrested the alleged perpetrator and took action to safeguard other children.
The inspectors were "surprised" that some officers accused children of crimes rather than treating them as a potential victim. Arrests had also been made for minor matters, such as pushing and shoving by siblings. The inspectors also heard that children were accused of lying when reporting an offence of sexual assault.
The report - In Harm's Way: the role of police in keeping children safe - concludes: "The level of child abuse and neglect is so high that it is difficult to process or comprehend. Responding on a case-by-case basis may be inadequate for the task.
"We found limited evidence that the police listened to children, and poor attitudes towards vulnerable children persisted in some teams. We also found that investigations were often inadequate, with insufficient action taken to disrupt and apprehend some perpetrators."
It also noted that although progress has been made "the gap between expected good practice and actual practice on the ground is significant".
The HMIC praised the "pockets of excellent practice" it found but stated that this seemed to be because of dedicated and professional individuals and teams, rather than a united, understood and applied focus on protecting children at force level.
The HMIC also hoped for a shift in old target-driven methods of policing, arguing that children must be placed at the heart of what policing does next.
Home Office minister Karen Bradley said: "This is difficult and complex work but police forces must do all they can to improve their response to child sexual abuse and exploitation.
"We are committed to ensuring police have the resources they need and we have prioritised child sexual abuse as a national threat, providing a clear mandate for forces to collaborate across force boundaries, to safeguard children and to share intelligence and best practice."
The other newly-launched reports were: Online and On the Edge: Real risks in the virtual world, about how police deal with the online child exploitation, and Building the Picture: An inspection of police information management.
In the report about potential online abuse the HMIC found that of the 124 case files examined across six forces, 52% were inadequate or needed improvement.
NSPCC chief executive Peter Wanless described this as "a damning indictment" of police forces.
He said: "Despite national commitments and the dedication of officers tackling these darkest of crimes, at a local level vital opportunities to protect children are being missed by the police."
Karen Froggatt of Victim Support, said: "Children are vulnerable and deserve to be given the utmost protection from sexual predators - this report shows that they are being let down by agencies that are supposed to protect them."
Chief Constable Simon Bailey of the National Police Chiefs' Council (NPCC) described the scale of child sexual abuse as "staggering".
The NPCC estimates that police will be investigating over 70,000 cases of child sexual abuse - an increase of 88% from 2012.
He pointed out that the HMIC's reports found that "protecting vulnerable people is a priority for all police forces, and considerable efforts and resources have been allocated to this end" but said there was still much more to do to provide the best service.
He said: "We are at a crossroads.
"We have got to fundamentally change our approach to policing so that our absolute focus is on working proactively with other agencies to protect the public from harm committed on or offline.
"This requires a cultural shift away from largely reactive policing that targets acquisitive crime with success measured by crime statistics and conviction rates.
"It must be supported by all agencies that work with children getting better at spotting signs of abuse, cruelty or neglect and intervening early to prevent harm.
"Police chiefs must lead this change but no-one should underestimate how much of a transformation this is.
"Changing the culture of 43 individual organisations with between 44,000 and 1,800 people working in them does take time."
David Tucker of the College of Policing said: "Helping forces to respond to child abuse is a high priority for the college and we have developed products to do this.
"We keep this area under constant review and will use this report to help us ensure that we give the best support we can to officers and their forces."