Thousands of parents in England are struggling to get subsidised childcare as they grapple with a glitchy website eight months after it was set up.
In some cases, money meant for fees has become stuck in tax-free childcare accounts, leaving some parents unable to pay their nursery bills.
Others struggled to apply for or reconfirm their free childcare.
The government says that fewer than 2% of the 320,000 parents who have opened accounts had encountered problems.
It added that earlier teething problems had been put right with extra resources and insists the website is running smoothly for the majority of parents.
But nursery and pre-school organisations say thousands of parents have experienced major problems using the HMRC-run website.
They have had to devote hours to helping parents resolve issues through repeated calls to the telephone helpline, they say.
And many parents have ended up relying on the goodwill of nursery bosses to keep looking after their children while they work, until compensation payments are forthcoming.
It comes after problems in the spring and summer when parents struggled to claim eligibility for either the 30 hours scheme for three and four-year-olds or the tax-free childcare - the government's two key schemes aimed at making childcare more affordable.
Debbie Raylan, a volunteer administrator at a nursery in Nantwich, said she had been supporting parents who had money locked in tax-free accounts and who were unable to reconfirm their right to claim free childcare.
"One lady I helped, had to make over 100 phone calls, literally, to get the problem sorted.
"This lady was looking at either giving up her job or finding someone else to look after her children. This is real life, it impacts on people."
One mother of two, Kathleen Shields, told the BBC her children's tax-free accounts had been wiped, and that helpline staff could not say when they would be up and running again.
Although, she was able to withdraw the funds she had paid in, she has been left more then £400 out of pocket for only two months' childcare costs as the government top-up cannot be received in the account.
"I would like to voice my disappointment," she said, "and highlight how difficult this makes things for hardworking families - mine and the countless others impacted by this."
She is claiming compensation.
Purnima Tanuku, chief executive of the National Day Nurseries Association, said she had heard from too many members for these issues to be confined to "teething troubles".
"It is causing ongoing problems," she said.
"Too many nurseries are saying they have parents who are struggling both to register and reconfirm their eligibility, something they must do every three months."
She said it had taken months for many nurseries themselves to register, with one taking more than a year to have its details approved.
"Here, the parents who had signed up for tax-free childcare were unable to use this towards their child's place at that nursery."
One of the key issues causing problems currently seems to be linked to the three-monthly reconfirmation.
In order to secure the government subsidy for the term that has just started, parents were required to reconfirm by 31 December.
Neil Leitch, chief executive of the Pre-school Learning Alliance, said: "It's incredibly disappointing that the long-running problems with the government's Childcare Service still haven't been resolved.
"This is an IT system meant to support a flagship government policy and yet, more than eight months after its launch, we are still hearing reports of parents who cannot do the simplest things.
"This is understandably causing much anger and frustration, something not helped by the government's insistence that all is fine with the website despite a wealth of evidence to the contrary.
"The government must get a grip on this problem once and for all, and ensure that the system it is asking parents to use is actually fit for purpose."
Ms Tanuku added that her organisation had been flagging up these issues on a regular basis with HMRC and attending advisory meetings regularly.
"Despite reassurances from the HMRC, these complaints are too commonplace and we are sure this is the tip of the iceberg."
Nicky Morgan, chair of the Treasury Committee, said problems seem to persist with the website despite HMRC saying it had resolved things.
"We've launched an inquiry into childcare, part of which will focus on the impact of these failures on the take-up of government initiatives that aim to make childcare affordable."
An HMRC spokesperson said: "More than 250,000 parents have successfully reconfirmed their eligibility. Almost all parents receive a response within five working days, and most get their decision instantly.
"If any parent is having a problem reconfirming or needs to speak to us, they should call us on 0300 123 4097."