Some neglected children are being left to suffer because their parents are being given too many chances by social care professionals, inspectors have found.
A review of 124 cases of neglect across England found a "mixed picture" in the quality of responses from local authorities and other agencies, Ofsted said.
Children were being left in harmful situations for too long in nearly half of the long-term cases examined, a report by the children's watchdog found.
There was a "lack of understanding" from local children's safeguarding boards (LCSBs) about the extent of neglect in their area, with some having "no clear picture" of the number of children in families where neglect may be a risk factor.
Some assessments focused "almost exclusively" on the parents' needs rather than the impact on their children, exposing youngsters to risk of further harm, it said.
Social care professionals did not "consistently challenge" parents who failed to engage with child protection plans, Ofsted said.
There was now "urgent need" for improvement in the quality of practice across the system, according to the watchdog.
The report concluded: "The quality of professional practice in cases of neglect is too variable, both between and within local authorities and by partner agencies.
"Some parents are given too many chances and some children are left in situations of neglect for far too long, with potentially very serious consequences. This is of serious concern."
The report, which focused on youngsters aged 10 or under, reviewed cases from 11 local authority areas and considered the views of parents, carers, council professionals and partner agencies.
The local authorities involved were Haringey, Lancashire, Liverpool, Manchester, North East Lincolnshire, Northumberland, South Gloucestershire, Surrey, Tower Hamlets, Wigan and Wolverhampton.
No children were found to be at immediate risk of harm at the time of the inspection, Ofsted said.
However, many of the social care professionals interviewed were not offered training to recognise the signs of neglect, the report found.
Despite examples of positive work, effective responses were not being shared widely across the profession, it said.
In some cases, professionals found it difficult to engage parents in child protection work due to a lack or "feigned" compliance which caused "significant delays" in more than a third of the long-term cases examined, the report found.
One director of children's services said some professionals see cases of neglect as "unremarkable in the context of so many other cases" and reported that social workers and schools may become "desensitised to neglect", according to the report.
Debbie Jones, Ofsted's director for social care, said: "It is widely accepted that neglect can have a devastating impact on the life chances of children and young people, and as recent high profile cases have shown, at its very worst, can be fatal.
"Some children live with serious and complicated difficulties in their families, and we need to examine what we can and should be doing to stop neglect far earlier in their lives.
"Absolutely vital to this is ensuring all social care practitioners are able to recognise the impact that neglect has on children, as well as being properly supported by skilled and experienced managers who are able to advise on help and intervention before the damage becomes irreparable.
"Social care professionals have a tough job to do. The pressure of increased workloads and the scrutiny on child protection means that dealing with this challenging area effectively can be extremely difficult.
"Despite this, it is clear that some children are not getting the help they need. LCSBs and local authorities must work to develop their understanding of neglect and to make sure that they are tackling this robustly and without compromise."
Among the examples of bad practice, a school failed to report early concerns about a six-year-old pupil who was arriving unwashed, wearing inappropriate clothing and occasionally wetting himself.
The child was brought to school by an older sibling and the mother had not engaged well with the school, the report said.
Another case saw police contact children's social care in early 2013 following a drugs raid at a house.
No drugs were found but concerns were raised about the "dirty" property where children were living, Ofsted said.
It emerged that a previous referral in the summer of 2012 from a school raised concerns that attendance was poor and the mother was not taking the child for his medical appointments.
There was found to be a history of domestic violence and the father admitted to using cannabis but the case had been closed after family support was offered, the report said.
The report also found two cases in which grandparents were colluding with parents to allow unauthorised access to children as well as being dishonest about the extent of drug use among parents.
Councillor David Simmonds, chairman of the Local Government Association's Children and Young People Board, said: "No child should remain in an unsafe or neglectful environment, and councils will not hesitate to intervene when children are thought to be at risk.
In cases where the situation is not clear-cut, social workers face incredibly tough decisions between leaving a child with a loving but struggling family or the risks of taking them into care.
"Social workers still too often hear about children at risk when it is too late, and it is vital that agencies like the police, schools and health come together locally to review and improve the way we all work together to deal with neglect."
A Department for Education spokesman said: "Today's report highlights the devastating consequences neglect can have on vulnerable children, which is why we've been clear that anyone working with children should take swift action when alerted to the early signs of abuse and neglect."
The department has also given the NSPCC more than £11 million "to run a comprehensive 24/7 advice and reporting service for those who have concerns about a child, and are developing training materials with the sector to help improve practice in this area", the spokesman added.