Bishops have called on the Government to urgently review its benefits freeze after a "deeply disturbing" report found poor working parents don't have the cash needed to look after children.
Low-paid families are taking a "double hit" because earnings are failing to keep up with inflation and many welfare payments have been frozen, the Bishop of Gloucester said.
The struggles faced by parents on the national living wage have been laid out in a report by Child Poverty Action Group (CPAG).
Families working full time are 13% or £59 a week short of the amount needed to provide their children with a minimum standard of living, according to the report.
The Cost Of A Child 2017 found the shortfall for lone and out-of-work of parents was even starker.
Figures show single parents working full time on the national living wage are 18% or £68 per week short.
Meanwhile, for non-working couples and lone parents relying on benefits, it stands at 42% or £187 a week, and 40% or £146 a week respectively.
The Bishop of Gloucester, the Rt Rev Rachel Treweek, said: "We have heard a lot about how earnings are not keeping up with inflation, but there is an urgency to recognise that low income working families are taking a double hit due to the four-year freeze in child tax credits and other benefits.
"With rising inflation, it is time to reconsider this policy in order to protect the living standards of the poorest families."
The Bishop of Durham, the Rt Rev Paul Butler, added: "Caring for our children should be at the top of our agenda as a society.
"We know that the first years of life are the most critical for the life chances of every child. So this report is deeply disturbing.
"Another fresh look at how we support working families with children seems to be required."
The report also warns these shortfalls will increase as inflation combines with the current freeze on working age benefits to put family budgets under new and greater strain.
It says that in the year to April 2017 the basic cost of a child from birth to 18, not including rent, childcare or council tax, rose from £72,596 to £75,436 for a couple.
For a lone parent this increased from £99,035 to £102,627.
According to the report, which also involved the Joseph Rowntree Foundation (JRF), government support with costs has also fallen.
For couples, child benefit plus the maximum amount of child tax credit now covers 94% of the basic cost of a child, compared with 98% last year.
For lone parents the proportion is 69% in contrast to 72% last year.
The report also says the freeze on benefits, implemented in 2016, and the uprating of children's benefits more slowly than price rises between 2012 to 2015, is impacting families.
For both working and non-working parents this combination has cost them £7.30 per week for the first child, and £5.80 per week each for the second and third child.
Chief executive of CPAG Alison Garnham said its research shows the benefit freeze means children will be "the main losers with the return of inflation".
"The cost of raising children is rising but for the first time in decades support for families is not keeping pace," she said.
"The result is a yawning gap between what ordinary families need for a no-frills living standard and what they actually have."
She said that shortfall will grow if inflation rises further with "damaging consequences for children", adding: "With the return of inflation the benefits freeze has become toxic for struggling families."
She said Chancellor Philip Hammond should use the Autumn Budget to invest in helping families with children, and that ending the benefits freeze is the first step he should take to re-balance the finances of ordinary families.
A Government spokesman said: "We're helping millions of households meet the everyday cost of living and keep more of what they earn.
"We introduced Universal Credit and increased the National Living Wage and tax free Personal Allowance to make sure it pays to be in work.
"We're committed to supporting parents with the cost of bringing up children, we've doubled free childcare, Child Benefit is available for all children in a household, and we continue to spend around £90 billion a year to ensure a strong safety net for the most vulnerable."