From Monday, 130,000 two-year-olds from the poorest families, or in care, are eligible for 15 hours' free childcare a week. Next year that number will rise to 260,000 children when parents who earn less than £16,190 a year and receive working tax credits become eligible.
Responding to the new policies, 4Children chief executive Anne Longfield said: "All the evidence shows that getting children off to a good start in life is a significant determinant of later success and the experience of high quality childcare is proven to support children’s early development.
"However, to deliver on these big aspirations government will need to continue to build the childcare infrastructure in this country. The government must be absolutely clear that they will only fund high quality childcare providers to deliver this programme, the evidence shows it is only high quality care that can deliver the impact for children that this programme aspires to."
Increased investment in childcare
Three and four-year-olds are currently entitled to 15 hours per week of 'early education' for 38 weeks a year.
The places can be in nursery schools, children's centres, day care nurseries, playgroups, pre-schools and with accredited child minders.
The £534m scheme allows two-year-olds from families in receipt of certain benefits - such as income support or income-related employment and support allowance - or those who are in the care of the local authority, to receive 15 hours of free childcare a week.
In a speech in Hammersmith, west London, Mr Clegg said the government would increase the money invested in the scheme to £760m in 2014/15.
Extend the helping hand even further
"From this time next year, we will extend that helping hand even further, doubling the number of youngsters getting a brighter start in life," said the Deputy PM.
"All the evidence shows that if you take two children - two five-year-olds hanging up their coats next to each other on the first day of school - the poorer child will already be behind their better-off classmate before a single lesson has been taught.
"Without this help, children suffer and the whole class suffers as teachers have to focus more of their efforts on children who are frustrated and left behind through no fault of their own."