Essex Police is carrying out an investigation at a Billericay nursery following concerns about treatment of some of the children in its care.
Detectives are working with colleagues from Essex County Council Social Care Department to investigate circumstances surrounding allegations at the Abacus Day Nursery in Orchard Avenue.
At this stage, there have been no allegations of sexual abuse.
Essex Police have been informed by Ofsted that the nursery has had its registration suspended and will be closed for up to six weeks.
Parents with children who attend the nursery are being contacted by Essex Police to advise them of the investigation and to talk to them about any concerns they may have.
A police spokesman said: "Essex Police takes the safety of children extremely seriously and will endeavour to keep parents and the community updated about the progress of the investigation as regularly as possible to ease any concerns."
A 49-year-old woman from Wickford was arrested by police at 6.30pm on Tuesday, February 18, and has since been released on bail.
The police spokesman added: "The safeguarding and well-being of the children is a priority for all of the agencies involved and Essex Police will continue to make enquiries with parents and other people who have an association with the nursery."