Nurseries will be subjected to spot checks under a radical overhaul of inspections unveiled this week.
Nurseries are currently told the month in which inspectors will call, but from next April they will receive no notice at all. Childminders will be given just "a few days" notice of when to expect a visit from the Office for Standards in Education.
The changes follow a consultation on early-years inspections, which drew 281 responses from parents and professionals.
Overall 94 per cent were in favour of inspections with little or no notice.
More than nine out of 10 wanted childcare to be assessed similarly to schools. In future, grades will be outstanding, good, satisfactory or inadequate.
Inspectors will focus on expectations for children set out in the government document Every Child Matters. Reports are likely to describe how nurseries and childminders keep children safe, promote their health, and help them enjoy learning.
The changes follow revelations in a TV documentary showing verbal abuse of children, poor hygiene and understaffing at several nurseries in England.
David Bell, the chief inspector, said: "As the world of education continues to change, so must the role of inspection."
A spokeswoman for the Department for Education and Skills said most nurseries were recently rated satisfactory or better. But she said the Government would never be complacent about quality and had promised unprecedented levels of funding for childcare over the next three years.
Tricia Pritchard, of the Professional Association of Nursery Nurses, said:
"We welcome unannounced inspections. Parents have a right to know if nurseries are maintaining standards. However, inspections with notice still have an important role to play."