Police, Ofsted and children's services have launched a joint investigation into the welfare of children at two privately owned nurseries.
Parents with children at Little Joes Day Nursery and Heworth House Day Nursery, both in York, have been informed about the inquiry.
The investigation relates to the running of the organisations and the quality of care provided - there is "no suggestion" that any sexual abuse has taken place.
A joint statement from Ofsted, City of York Safeguarding Children Board, City of York Council and North Yorkshire Police confirmed they were carrying out joint inquiries into Little Joes, on Fishergate, and Heworth House, on Melrosegate.
The statement said: "The inquiries relate to the running of the nurseries, the quality of care and the welfare of children who attend the nurseries.
"City of York Council has written to all parents whose children currently attend the nurseries, to inform them of the inquiry and to assure them that they will be kept fully informed of all developments."
It continued: "The inquiry is in the very early stages and it is therefore not appropriate to comment further at this stage, however, there is no suggestion that any sexual abuse has taken place."
Little Joes takes children from birth to eight years old and has separate pre-school, toddler and baby units. It was last inspected by Ofsted in September 2008, when it was rated "good" overall.
The nursery has a maximum capacity for 51 children and employed nine staff at the time of the last inspection.
Heworth House was inspected by Ofsted in May this year, when it was rated "satisfactory".
It is registered to take children from birth to five years and has a maximum capacity for 30 children. It employs nine members of staff.
The nursery's prospectus states: "It is important to us that the children in our care receive the attention and stimulation they require, therefore the nursery consists of qualified nursery nurses and nursery assistants.
"Children's safety and well-being is paramount, we have various policies and procedures which are regularly reviewed and updated."
Any parents who have concerns can contact the City of York Council's Family Information Service advice line between 8.30am and 5pm on 01904 554444, or by emailing fisyork.gov.uk