As many as 140,000 disadvantaged two-year-olds could have free nursery places under a scheme planned to be rolled out in England.
Plans to give 15 hours of free "early education" a week to all two-year-olds from poor homes were announced last year but details have now been set out.
A pilot scheme, first started under Labour, is due to be extended nationwide from September 2013.
Deputy Prime Minister Nick Clegg said all children needed the best start.
All three and four-year-olds are currently entitled to 15 hours of early education for 38 weeks a year.
This can be in nursery schools and classes, children's centres, day care nurseries, play groups, pre-schools and with accredited child minders.
Under the new plan, which is out for consultation, parents will be able to use their allocated time flexibly, between 07:00 and 19:00.
So for example, they could have seven-hour slots for two days a week, to make it easier for them to work.
'Balance work and home'
Ministers say access to early education improves the life chances of poor children by helping them develop and get ready for school.
Disadvantaged children are far less likely than others to do well in education.
Under the pilot, 20,000 two-year-olds received the free provision in a year.
Extending it to all two-year-olds in low income families would mean 140,000 stood to benefit every year, the government said.
Mr Clegg said: "I want us to give every child the best possible start - so free education for toddlers from the most disadvantaged homes will now be a right and not a privilege.
"Crucially the extra care will be flexible and easy to access. Parents across the country are bending over backwards to balance work and home. The coalition wants to help in whatever way we can."
Families where children would qualify for free school meals are those who would be entitled to the free care.
The government has also published a breakdown of how many two-year-olds would qualify in different parts of England.
More than 20,000 would be eligible in London and a similar number in the north-west of England.
Nearly 17,000 in the West Midlands would qualify and a similar number in the South East. In Yorkshire and the Humber the figure is nearly 15,000 and in the North East it is nearly 8,000.