More than 100 parents in Plymouth were last night being contacted by police attempting to establish how many children might have been sexually abused at a nursery by a female employee, after she was charged with a series of sexual offences, including four counts of sexual assault.

Vanessa George (39), who worked at Little Ted's Child Day Care Unit in Laira in the east of the city, was also charged with three counts of making and distributing indecent images of children.

She was arrested by police at her home in nearby Efford at around midnight on Monday, after Devon and Cornwall Police received a tip-off from another force.

During the raid on her home, officers seized her mobile phone and computer equipment. A cursory search of the phone uncovered a “small number” of indecent images, but officers said yesterday they feared “hundreds or even thousands” more might be stored on her computer.

From the nursery, they recovered a computer disc which contained more than a dozen images of “a serious nature”.

George, who lives with her husband Andrew and their two teenage daughters, has worked at the nursery for at least two years. She faces two counts of sexual assault by penetration, two counts of sexual assault by touching, and three further counts of making, possessing and distributing indecent images of children.

At a press conference yesterday, Devon and Cornwall Police confirmed that some of the images had been taken inside the nursery, but added it was “impossible to say” where all of them originated.

Their investigation is focusing on the alleged exchange of material between George and Colin Blanchard (38), from Littleborough, near Rochdale. On Tuesday, Blanchard appeared at Trafford Magistrates' Court charged with the possession and distribution of indecent images.

It is understood that police investigating Blanchard contacted their colleagues in the Devon and Cornwall force at 9pm on Monday, after discovering emails containing images of abuse allegedly sent by George. In some of the images, George can be seen wearing a T-shirt with the nursery's logo on it.

Police said they had struggled to identify the children in the pictures, many of whom were shot in close-up, and admitted it may never be possible to correctly identify some of the victims.

Chief Superintendent Jim Webster, of Devon and Cornwall Police, said: “This investigation is fast-moving and now confirmation has been received of evidence leading to the charges today.

“It is a significant and disturbing situation, and the position is made more difficult that identification of the children is very difficult. There are many that contain the images of torsos.

“As we go through the painstaking task of identifying who may be concerned, we are focusing on communication with families.”

Russ Middleton, head of CID, added: “It's safe to say we believe some of the images were taken in the nursery. At this time we have been unable to identify any images of individual children and it is right to say some images may never be identified.

“Our priority is to build up a close relationship with potential victims and focus on children contained within the images.”

On Tuesday, police called a meeting in Plymouth during which they spoke to around 100 parents and people associated with the nursery. Plymouth City Council's director of children and young people's services, Bronwyn Lacey, addressed the gathering.

The nursery is responsible for 60 babies and toddlers aged between one and five, but children up to the age of 11 may also attend breakfast and after school clubs.

George remained in custody at Charles Cross police station in Plymouth yesterday. She is due to appear at Plymouth Magistrates' Court this morning.