The Prime Minister has admitted it will "take time" to get the new childcare plans right.
Speaking on This Morning, David Cameron said: "It's going to take time to get this right because obviously we need an expansion of the childcare sector, we need more nurseries, more of these places to open so we're working with them to expand."
He added: "We need them to expand so we're going to start talking to them immediately about what's the best way of making sure that they're being properly paid for, the childcare that they provide, so that we can expand the number of places."
The government grant to childcare providers for the existing 15 hours a week of free childcare is already "grossly underfunded", the Pre-School Learning Alliance has said.
Research for the charity suggests the government's plan to double this childcare would cost around £195bn a year, but funding at current rates amounts to £1.7bn - a potential shortfall of £250m.
Chief executive Neil Leitch said: "Simply raising funding rates by an arbitrary amount won't be enough - it is absolutely crucial that the Government ensures that the hourly rate of funding actually covers the cost of delivering funded places. Anything less risks destabilising a childcare system that is already struggling to stay afloat."
He warned an increasing number of providers may withdraw from the free childcare system if more money is not made available.
Speaking on the BBC Radio 4 Today programme, Mr Leitch added: "There are many nurseries that can't physically extend their number of hours. They may operate in a church hall or community centre. Nobody has considered whether in fact they will be able to offer the 30 hours."
Plans to double the free childcare for working parents in England have been brought forward by a year.Read the full story ›
All three main political parties "need to invest in families" as they are the UK's most valuable asset, a children's charity has warned.
Anne Longfield, 4Children's chief executive, said the family vote would be "key" in the 2015 general election and called on MPs to improve childcare.
All the main political parties know that the family vote will be key at the ballot box next year.
With half of people calling for more support for children and families, it is clear that the scale of ambition needs to radically change.
Families are looking to all the parties to set out what they will do to make Britain great for children and families.
It is time for a real shift of ambition to give children and families the support they need to flourish. Families are our country's most valuable asset and political parties need to invest in them.
Almost half of Britons feel family life has become harder over the last 30 years, a YouGov poll for a children's charity has found.
Some 46% said family life was harder in 2014 than it was three decades ago, according to charity 4Children.
Even more parents (49%) wanted the Government to do more to help them balance the demands of work and raising children in the 21st century.
Whichever party wins next year's general election should open schools from 8am to 6pm to help struggling parents cope, 4Children said.
They also wanted to see free childcare extended to 25 hours a week for all children aged between one and four by 2024, and for Sure Start to be turned into "children and family community hubs".
Parents of a five-year-old girl starting full time education said balancing earning money with wrap around childcare was "a juggling act".
Barry Woodham and partner Emma Harrington told Good Morning Britain they have been forced to hire a childminder to care for their daughter Ruby when she enters full-time education in October.
Some 51% of parents struggling to find childcare said their employer was helping out by allowing them to work flexibly, a poll has found.
Research carried out by charity 4Children found:
- 53% of parents were allowed to work fewer hours to meet the demands of childcare.
- 33% of parents work from home some of the time.
- However, 27% had not received any assistance from their employer.
Almost half of parents struggling to find childcare ahead of the new school year have considered leaving their jobs to look after their little ones, a study has found.
An investigation carried out by a children's charity found single and young parents were struggling the most.
Some 61% of single parents and 63% of parents aged between 18-34 who had been unable to organise the childcare they need were considering giving up their job, said 4Children.
The survey of 500 parents with children of primary school age also revealed the need for schools to help provide care - 87% of parents whose child's school did not have an after school club wanted one.
A group of parents agreed they would not leave their young children unsupervised during their school holidays if they were unable to find suitable care for them.
Good Morning Britain spoke to parents dropping their children off at a school holiday club and found all of them would not leave their youngsters to look after themselves while they went off to work.
Some 25% of parents told a Good Morning Britain and OnePoll survey they had given up work to care for their child because they were unable to find a suitable alternative.
The poll also found:
- Over a third have ever left their child/children (aged between 4-16) home alone.
- Almost a fifth (19%) say they consider a child aged 9 and under to be safe to be left alone.
- One quarter spend more than £101 on childcare every week during the summer holidays.
- The average spend on summer childcare is £62.52 per week.