Nurseries face on-the-spot inspections as part of a new regime intended to raise standards and cut red tape, the chief inspector David Bell said this week.
The change is one of five proposed in a consultation paper which aims to ensure nurseries and childminders are in step with the aims of the Green Paper Every Child Matters.
The watchdog had already considered giving nurseries short-notice inspections before a BBC TVundercover documentary last month showed staff shouting at children and cases of poor hygiene in some nurseries.
The new framework, which introduces self-evaluation to early-years inspection, is modelled on plans for school inspections which were published earlier this year.
Ofsted said inspectors will use the new regime to judge what it is like to be a child in each nursery setting.
From April next year, nurseries and childminders will have to fill out a "simple" self-evaluation form prior to inspection.
Nurseries and childminders at present receive advance notice of the month in which the inspection will take place, but not of the exact day.
Under the new regime, nurseries will receive little or no notice and childminders a minimum notice period simply because inspectors need to check when they will be at home.
Providers will be graded on the same four-point scale as schools, ranging from inadequate to excellent.
Inspectors will assess state-funded nursery education against the aims of the foundation stage.
Rosemary Murphy, chief executive of the National Day Nurseries Association, said: "We support proposals for minimal notice inspections - good childcare settings should have nothing to fear from this.
"Parents must, however, be aware that regulation and inspection will never guarantee quality. We need to develop a well-paid and highly-qualified workforce. This will never happen unless we see massive government investment into the sector."
The consultation will end on September 30.
* Young children are missing out on vital pre-school education because of a postcode lottery, a report by an influential committe of MPs said this week.
The public accounts committee said many parents still could neither find, afford nor access pre-school places, particularly in London and in some deprived "pockets".
The MPs did acknowledge that spending on under-fives has risen from pound;2 billion in 199798 to pound;3.6bn in 20023.