Ministers have been accused of creating a childcare crisis, after a survey showed Sure Start centres in England are cutting back on places, reducing numbers of qualified staff and charging for services that were previously free.
Some 15% of Sure Start centres questioned by the charity 4Children said they were "struggling" with budget cuts, while 50% said their finances were less sustainable as a result.
The charity warned that, without solid funding arrangements from central and local government, centres may not be able to continue to cope in the long run.
The survey was released as the government's Childcare Commission launched a consultation on how to improve the accessibility and affordability of childcare.
Prime minister David Cameron, who announced the establishment of the commission last month, said it wanted to hear the ideas of "everyday experts - parents, childminders and nursery owners - on how we can make the system better and more affordable".
But Labour said that the 4Children survey showed that Mr Cameron needs to "get a grip" on childcare.
The survey found that:
- Some 20% of Sure Start centres questioned are charging for services which were formerly free
- More than half (55%) no longer provide any onsite childcare, and those that do are providing fewer places. Half (50%) of those offering places say they are now oversubscribed
- Nearly 20% have cut the numbers of qualified teachers and a further 20% say they will have to reduce childcare staff
- Greater use is being made of volunteers, with 60% increasing numbers of voluntary workers and 50% asking them to work longer hours
Labour's spokeswoman for children, Sharon Hodgson, said: "Before the election David Cameron said he was committed to Sure Start, yet he has allowed hundreds of centres to close and the remaining ones to be hollowed out. The prime minister now needs to take urgent action to get a grip on Sure Start and the childcare crisis his government are creating.
"The fact that more services are being charged for and staff are being laid off shows the effect of the government's decision to cut funding for Sure Start by 20%.
"They are removing a much valued service at a time when the cost of childcare is rising."
4Children said it was "concerned" about the long-term impact of the removal in 2011 of the duty on Sure Start centres in deprived areas to offer childcare places.
The charity's chief executive Anne Longfield said: "Children's centres across the country have demonstrated resilience and creativity, and enjoy overwhelming support from professionals working within the sector, parents and communities.
"Now must be a time for development, not decline. There is huge potential for children's centres to play their full part in delivering early help and intervention. The task is enormous and it is essential that local and central government continue to provide sustained funding.
"Gains made must not be lost. Children's centres must now be put at the heart of delivering early help and intervention. It is for local authorities, professionals and communities to come together and nurture the potential of Sure Start children's centres across the 0-19 age range."
A Department for Education spokesman said: "There is enough funding in the system to retain a very strong national network of Sure Start centres - open to all but targeted much better at the poorest children.
"We've never hidden the fact that this is a tight spending settlement. It is down to councils to judge best how to prioritise budgets; cut back waste to give the taxpayer value for money; and retain a high quality, effective childcare - including 'clustering' to reduce overheads and target families in real need.
"Local authorities have a statutory legal duty to provide sufficient children's centre provision and childcare for all the families in their areas - no ifs or buts. By law, they must fully consult local people properly before closing or making any significant changes to children's centres."
Launching the Childcare Commission consultation, families minister Sarah Teather and work and pensions minister Maria Miller said it will look at ways to encourage provision of out-of-hours childcare as well as identifying unnecessary regulations which get in the way of care.
Ms Teather said: "We have an ambitious programme to extend the entitlement to free hours at a nursery or childminder to those two-year-olds who most need it. More than a quarter of a million two-year-olds will benefit from learning through play and stories in just two years' time.
"So it's really important that we get this right and I hope we will receive many strong and fruitful ideas."
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