Police investigating how three children came to suffer broken bones at a nursery in Nottinghamshire said on Tuesday they had made an arrest over a suspected sexual assault at the centre.
They said the arrest, made last Friday, was a new line of inquiry after information was given to detectives about an incident that took place last year.
"Prior to this, neither Notts Police nor Ofsted were aware of any alleged sexual offences having taken place at the nursery," a spokesman said.
"The individual concerned has been questioned by detectives and released on police bail pending further inquiries," he said.
Police and Ofsted, the body which oversees nurseries, launched a joint probe last month into the Rocking Horse Nursery in the village of Plumtree after a child was taken to hospital after suffering an unexplained fracture.
Subsequent enquiries established that two other children who attended the nursery also had broken bones.
Two people were arrested in connection with the injuries and another three were interviewed under caution.
The nursery has been closed while the investigation is carried out.