Deputy Prime Minister Nick Clegg said he was "absolutely passionate" about improving the quality and availability of childcare but "we have got to get this right".
Asked during his phone-in show on LBC 97.3 if the Prime Minister was aware of his concerns, Mr Clegg said: "We have been talking about this for weeks and weeks."
He said: "I have got young children ... they have been through nursery so I know how much parents will really care that we get this right in terms of improving both the affordability of childcare, which we must do, but also the quality.
"What the Department for Education did is they consulted and they said is it possible to have an adult look after more children, so instead of four two-year-olds ... go up to six two-year-olds. I think four is already quite a handful, just imagine if they go up to six.
"Can you do that at the same time as raising quality? A lot of people basically got back in the consultation and said this isn't going to work, particularly for very small children, it isn't necessarily going to be passed on in terms of cost savings to parents."
Shadow education secretary Stephen Twigg tweeted:
A new Government split has emerged this morning on proposed changes to childcare regulations.
Neil Leitch, the Chief Executive of The Pre-School Learning Alliance said parents on the whole are "overwhelmingly opposed to those reforms."
"The vast majority of parents", he added, "recognise its very difficult to take care of six two-year-olds in stead of four."
Nick Clegg "remains to persuaded" of the benefits of the government's childcare reforms. His spokesman said:
The delivery of good quality affordable childcare is one of Nick Clegg's biggest priorities in government. He has looked very closely at proposals to increase the number of children each adult can look after - and at the very serious concerns raised by parents and childcare providers in the recent government consultation.
Nick remains to be persuaded that this is the right thing to do for very young children. Or, crucially, to be persuaded that this would actually help families with high childcare costs.
The government's plans to increase the number of children that nursery workers and childminders can care for were announced in January.
The new rules are due to come into force in England in September.
- One-years-old and under: Current ratio of adults to children is 1:3, this would change to 1:4
- Two-years-old and under: Current ratio is 1:4, this is due to change to 1:6
- Three-years-old and over: Current ratio is 1:8 or 1:13 (if teacher led), this would remain the same
Deputy Prime Minister Nick Clegg has said he "remains to be convinced" of the government's plans to enable nursery staff and childminders to take care of more youngsters.
From September the ratio for under-ones is due to rise from three per adult to four.
The proposals have run into fierce opposition from experts and unions.
People in Britain rate the quality of childcare highly, despite it being expensive, new research has shown.
But many believe that care for the nation's elderly is below par and are concerned that the care for their elderly relatives is substandard.
A study of reviews left on feedback website the Good Care Guide gave childcare mainly positive feedback.
Care for the elderly was viewed as needing improvement, with nearly three quarters (71%) of negative reviews on the site directed towards care in the home provided by homecare agencies and care homes.
The Good Care Guide, launched a year ago, works like Trip Advisor, allowing people the chance to find, rate and review care providers.
The site analysed more than 2,000 reviews, describing those with 0-3 stars as negative, and those with 4-5 as positive, and found there was one negative for every eight positive.
Mumsnet co-founder Justine Roberts' response to the Government's announcement of future financial help for working parents is "thank God they're doing something".
But she questioned whether parents who earn just under £300,000 should be given extra money by the state.
Parents will be able to claim up to £1,200 per child under new childcare plans unveiled and promoted today by David Cameron and Nick Clegg.
The Coalition leaders met parents at a nursery in south London with the welcome news that from 2015 they will have 20 per cent of rising childcare costs covered.
But, as ITV News' Deputy Political Editor Chris Ship reports, the delay for the new funding pledge to take effect has been criticised.