Vulnerable children are being failed by "unsatisfactory and inconsistent" protection services across England, according to a new report.
The chair of an influential House of Commons committee said it was "horrifying" that more than 75% of local authority child protection services were found to be inadequate or requiring improvement.
The National Audit Office (NAO) found that demand for help and protection is rising, with a 124% increase in the past 10 years in the number of serious cases where a local authority believes a child may be suffering, or likely to suffer, significant harm.
But almost 80% of councils inspected by Ofsted over the past three years failed to meet the "good" rating for support to children needing protection, said the NAO.
Some 26 out of 152 child protection departments are subject to Department for Education intervention after being rated "inadequate".
Despite the Department for Education recognising the existence of a problem in 2010 and taking action on the recommendations of the following year's Munro Review on child protection, the services offered to children by local authorities are still "not of good enough quality", the NAO report found.
Meg Hillier, who chairs the Commons Public Accounts Committee, said: "Children in need depend on child protection services to get it right for them where other adults in their lives have failed.
"It is horrifying that over three-quarters of local authorities' child protection services are inadequate or require improvement to be good.
The NAO found that thresholds for assistance varied from area to area, meaning some children were left at risk while others were inappropriately referred for help.
The Department for Education and local authorities lacked the data needed to understand which approaches would provide the most effective help and protection.
The report found that the department does not intervene early enough in failing children's services and faces "significant challenges" to transform standards by its target date of 2020.
An NSPCC spokesman said: "This damming report re-exposes some gaping holes in local authorities' ability to deliver effective services and protect vulnerable young people, while also revealing the vast extent to which support varies across the country."
A Department for Education spokeswoman said: "We are taking tough action to drive up standards in children's services across the country, stepping in when councils aren't doing well enough and linking them up with better performing local authorities to share best practice.
"We have also cut red tape so that social workers can spend more time actually supporting families."