He also announced parents of children on free places can drop their children earlier and collect them later.
He told BBC Breakfast: "We're revolutionising the early start our children get in life - there will be more free childcare, it will be higher quality, and it will be more flexible for parents
"Every child should have a fair crack at the whip from the start and be able to go on to fulfil their potential.
'By getting things right from the off we're making sure our youngsters are ready to learn when they start school so that they get the most out of their education."
More than 800,000 three and four year olds nationally are currently eligible for 15 hours per week of free early education.
The plan had been to extend this to 150,000 two year olds from the poorest families from September 2013, rising to around 260,000 in the following year.
But Mr Clegg said that a £3million trial – affecting around 1,000 children - will now start in September in 10 trial areas.
The time when parents can pick up and drop children is also being increased from 8am to 7am, and from 6pm to 7pm.
Parents will also be able to spread their free nursery places over two, rather than three, days, which will allow them to leave their children for longer on individual days.
Following a consultation, Mr Clegg announced that the first areas to benefit, in September this year, will be Blackpool, Cornwall, Greenwich, Kent, Lambeth, Lancashire, Newcastle, Northamptonshire, Peterborough and Rotherham.
New guidance will also make clear that nurseries cannot make the free childcare conditional on parents also taking up additional paid-for hours.
Is this strategy about helping parents back to work - in which case why not start subsidised childcare after maternity leave?
Or is it about helping children who might fall through the cracks to prepare for school?
Tell us what you think?