The All-Party Parliamentary Group for Children (APPGC) report raises concerns about varied thresholds across councils for a range of support for children at risk of harm or in need of help.
The report includes a survey of 97 directors of children's services (DCSs), which found that around three quarters (74 per cent) believe thresholds for supporting children in need differ across councils.
Just under two thirds (64 per cent) of DCSs said there are variations in thresholds for deciding when to put a protection plan in place because a child is at significant risk of harm. Meanwhile, around half (49 per cent) said there are differences in terms of when councils apply for a care order.
In addition, 83 per cent of DCSs said that thresholds for early help varied across councils. The APPGC report concludes that "protecting children has become a postcode lottery".
"The level of need a child has to reach in order to access support was found to vary across the country," states the report.
"Inconsistency appears to be particularly stark in relation to the provision of early help and wider preventative services."
"Local authorities should be empowered to set local priorities that respond to the specific needs of their populations.
"However, the APPGC believes that a postcode lottery in children's social care is unfair to children and families and is not acceptable."
The APPGC's report also details the results of a survey of 1,700 social workers, in which 70 per cent felt children in need thresholds had risen and half said that child protection plan thresholds had increased in recent years.
Evidence submitted to the inquiry by social workers and researchers indicates that funding constraints are influencing decisions on whether to intervene to support children.
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"It is unacceptable that children's safety is potentially being undermined by a lack of sufficient resources," states the report.
Among recommendations made by the APPGC is for government to improve funding for children's social care and put in place a sustainable, long-term funding settlement for early help services.
It also wants ministers to launch a consultation on whether councils should be legally obliged to offer early help.
"Children and families around the country with the same urgent needs are getting significantly different levels of help, and in some case, no support at all," said APPGC chair and former children's minister Tim Loughton.
"This is true for families who struggle to cope on low income, living in poor housing which puts their children's health in jeopardy. It's true for children who are harming themselves yet are kept waiting for treatment because they aren't at immediate risk of suicide. These people need help now, regardless of where they live.
"In some places, the pressure on children's services is so acute it is leaving social workers feeling that the only tool available to them to keep a child safe is to remove them from their family.
"As a result, families may look at these skilled and caring professionals with mistrust. But this is wrong. It is the woeful underfunding by government of a proper breadth of social care interventions that is to blame."
Children's minister Nadhim Zahawi said: "We want every child to grow up with the right care and support so they have the opportunity to fulfil their potential. That's why our ambitious children's social care reforms are improving services nationally so that children receive the same quality of support regardless of where they live.
"This government has made £200bn available to councils for local services, including children's services, up to 2020, and we are developing, testing and sharing innovative ways of supporting vulnerable children and families through our £270m children's social care programmes.
"These include projects that help families at risk of breakdown, reducing the need for child protection measures, repeat referrals to children's services or entry to care."