Failing nurseries and pre-schools are to face closure if they do not rapidly improve, Sir Michael Wilshaw has announced.
Under a major shake-up of early years inspections those that fail to raise their game will have their registration cancelled, the Ofsted chief inspector said.
The move could affect thousands of nurseries and pre-schools currently caring for young children in England.
Sir Michael also raised fresh concerns about qualifications among those working with babies and toddlers, saying it is an "absolute nonsense" that more exams are needed to work with animals than young children.
Sir Michael announced that from September, Ofsted will only consider a rating of good or outstanding to be acceptable for nurseries and pre-schools. The satisfactory judgment will be scrapped and replaced by "requires improvement" - a change already made to school inspections in England.
Nurseries and pre-schools which are judged to "require improvement" will face more inspections and have up to four years to raise standards. If they are not rated "good" after two inspections they are expected to be considered "inadequate". And "inadequate" nurseries and pre-schools that fail to improve will face having their registration cancelled, effectively closing them down.
The move comes amid concerns of the inspectorate that many pre-schoolers do not have access to good childcare.
"They will have four years to become good", Sir Michael said. "Four years is a long time in a child's life. If they haven't improved by then, they are likely to be judged inadequate and we are going to recommend closure and deregistration."
Ofsted figures show that as of the end of August last year, up to 243,400 children were being cared for by nurseries, childminders and pre-schools that were not yet considered good. More than two fifths of early years educators were judged no better than satisfactory at their last two inspections, and over one in 10 had dropped a grade, according to the watchdog's annual report, published in November.
Sir Michael said that one of the biggest problems with early years education is that too many of the workforce are under-qualified. He added: "We simply must get better qualified people working in the right areas in this sector."