Children are "force-fed, shouted at and roughly handled and restrained" in some pre-school centres, Jacquie Roberts, chief executive of the Care Commission, told the early years conference.
Joint education and care inspections with HMI of some 600 centres since April last year were already showing their worth, Mrs Roberts said. But some children "are being brought up in fear and learn the wrong things".
Most pre-school inspections showed strong practice but some centres still failed to meet national standards. Staff shortages and a high turnover of assistants meant that some centres failed to provide the interaction with adults that children needed.
Graham Donaldson, senior chief inspector of schools, confirmed this view:
"There are still centres where play is poor and children do not have the quality and experience they deserve."
Mrs Roberts said practice was good where care and education linked, groups were small, expectations consistent and the environment safe and healthy.
Planned age-appropriate activities and free play were other factors.
"Everyone knows in their bones that care and education are inextricably linked," she said. It was therefore logical that the Care Commission and HMI worked together in the pre-school sector.
Mr Donaldson said there continued to be "huge public interest" in early years education and care and there was now a close and effective working partnership on inspection teams.
All 2,500 pre-school centres are due to be inspected by 2006.