A survey of more than 1,200 health visitors found that 43 per cent believed they may not recognise a child in need until it's too late as a result of rising demands in recent years.
The findings showed health visitors are increasingly having to deliver "child protection social work-by-proxy" due to increasing child protection thresholds within children's services departments.
The Institute of Health Visiting (IHV), which conducted the annual study, has previously warned that health visitor numbers are below safe levels, with the health visitor survey report showing numbers have dropped below levels in 2011 when the government introduced a new scheme that boosted numbers by more than 2,400.
At the time in January 2011 there were 7,906 health visitors, rising to 10,309 by the end of the health visitor implementation plan in October 2015. By July this year levels had dropped back down to 7,852.
Nearly half (44 per cent) of health visitors said they are now working with caseloads of more than 400 children, up from 28 per cent in 2015 when commissioning of their service transferred to local authorities. The government mandates health visitors deliver five assessments to each child in England by the time they are two and a half years old
IHV recommends a maximum of one health visitor to 250 children to deliver a safe service. Respondents warned that rising caseloads are leading to a dilution of the universal offer, with 45 per cent saying they could only provide continuity of care to the most vulnerable families.
The report stated: "Health visitors are increasingly focused on the most vulnerable children and families at the expense of the five reviews and that the Healthy Child Programme is being implemented in an increasingly ‘targeted' manner."
"This leaves ‘invisible' the growing numbers of vulnerable children who remain unknown to other services."
The survey also found that many health visiting teams are delegating reviews to non-registered practitioners without health training, and some are not being carried out at all.
It found that while new birth and six-to-eight week reviews were reported as almost all being undertaken by qualified health visitors, 65 per cent of nine-to-12 month reviews and 79 per cent of reviews once a child was two or older were delegated to other staff.
The report states: "The qualitative comments of respondents indicate concern that this is now routine practice and therefore not true delegation (based on a professional rationale), but rather has become a bureaucratic imperative."
IHV executive director Cheryll Adams said the findings were "hugely worrying".
"Many of the issues that health visitors are trained to assess during these contacts with families are hidden and are easily missed by less-qualified practitioners," she said.
"This means that these issues may be much harder and more costly to address by the time that they become conspicuous.
"It is about much more than the number of contacts, it's the quality of those contacts that matters - having enough time to listen to family concerns and to act on them.
"This is an unacceptable situation for English children as it has implications for their wellbeing across the life course."
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The IHV has called for government to reinvest in public health services and create a joint integrated commissioning framework between local authorities and the NHS for universal children's health services.
The call has been backed by the president of the Royal College of Paediatrics and Child Health Russell Viner.
"Health visitors play a vital role in public health and prevention," he said.
"They provide crucial health advice to parents, identify and put interventions in place for children with health, educational and potential safeguarding needs, and help to prevent accidents, injuries and more serious problems later in life."