Childcare providers have raised concerns about moves to increase the number of pre-school children that nurseries and childminders can look after.
As part of coalition efforts to cut childcare costs, staff are to be able to take charge of six two-year-olds rather than four, while the ratio for under-ones will go up from three to four.
Education minister Liz Truss outlined the changes alongside reforms that will see higher qualifications required of those caring for pre-schoolers.
She said the Government wanted to introduce graduate-level "early years" teachers and create an Early Years Educator qualification requiring practical experience and at least a C grade in English and maths GCSE.
But the Pre-School Learning Alliance denounced the Government proposals as a "recipe for disaster", claiming the vast majority of childcare providers were against relaxing the adult-to-child ratios.
Chief executive Neil Leitch said: "We are absolutely appalled by this fixation to alter ratios, despite the fact that those working in the sector are universally opposed to the proposal.
"This is a recipe for disaster and I hope those making this decision will be as enthusiastic in answering questions from concerned parents and the media when the consequences of their actions come to the fore."
Liz Bayram, joint chief executive of the National Childminding Association, said increasing ratios would only be justified if accompanied by new systems to help minders ensure every child still received "a high quality experience".
"We know many of our members do not use their full ratio level at present, because such young children rightly demand high levels of individual attention and care to thrive," she said.
Dame Clare Tickell, chief executive of Action for Children and chair of the Government's Independent Review into the Early Years Foundation Stage, said children needed "dedicated one to one time with staff to help them learn and develop, and we would be concerned if this is compromised".