Many parents say they are simply unable to work
A quarter of parents on low incomes are unable to work because they cannot afford childcare, research conducted for Save the Children suggests.
Some 28% of families, with children under 18, earning less than £15,000-a-year after tax said they could not work because childcare cost too much.
The charity says income could be raised via tax credits or the minimum wage.
Separate research suggests holiday childcare costs in Britain rose 8% over
the last year to average £87.43 a week.
The government has urged parents to make sure they are claiming all the financial help available to them.
YouGov surveyed 2,055 people during July for Save the Children.
Dr Jason Strelitz, the charity's UK poverty spokesman, said: "Many parents on low incomes simply can't afford to go to work.
"The costs of childcare are so high that by going to work they lose more money than they make.
"Many parents have to leave their jobs to look after their children."
He added that most parents in poverty "want to work, but with no-one to look after their children they can't".
The problems faced by a quarter of those on low incomes compares with just 9% of parents with take-home pay of more than £15,000 who felt the same way, according to Save the Children.
Children's Minister Beverley Hughes said the government recognises childcare, after school and holiday clubs can be expensive for parents.
She said the government was "spending £3.5m a day through tax credits to support parents with these costs" to counter the problem.
She added: "Parents are also supported with child benefit, which provides help to 7.5 million families and 13.3 million children and Budget 2008 announced Child Benefit for the first child will increase to £20 from April 2009."
Stressing that those with children should claim "all the financial help available", she said that parents can get up to 80% of childcare costs back in tax credits each week, including during school holidays.
But Liberal Democrat children spokeswoman Annette Brooke said some parents have found that the "only affordable option" is to give up their jobs in order to look after their children.
"If the government really expects parents to go back to work, it needs to ensure that all parents have access to good childcare," she said.
Meanwhile, an annual survey by the Daycare Trust on the cost of holiday childcare, found prices increased by 10.1% in England, 5.3% in Wales, and 8.6% in Scotland in the last year.
The findings also highlighted concerns expressed by many parents that there was a shortage of holiday childcare in their area, particularly for children aged over 12 and for disabled children.
Disability charity Scope said the figures were a concern.
Its chief executive, Jon Sparkes, said: "Rising costs and lack of availability are an additional issue for families of disabled children, who also face challenges relating to poor accessibility of childcare settings and a lack of appropriately trained carers."