Vanessa George, 39, who had worked at Little Ted's nursery in Plymouth, pleaded guilty last week to seven charges of child abuse and six charges of taking indecent images of children.
She will be sentenced next month, alongside Angela Allen, 39, and Colin Blanchard, 39.
Police said that despite repeated questioning, Ms George had refused to reveal the identities of the children she had abused. They believed that up to 30 children from the nursery are victims.
Judge John Royce called on Ms George to reveal their names before she is sentenced next month.
Plymouth City Council's local safeguarding children board are carrying out a serious case review, which children's secretary Ed Balls said he expected to be completed as soon as possible.
Purnima Tanuku, chief executive of the National Day Nurseries Association, said, 'NDNA, like nurseries across the UK, is shocked and appalled by this news. Our thoughts are with the families who will be extremely distressed during this time, and we hope that the authorities conclude the case swiftly.
'Many parents will no doubt be worried by the headlines and we would urge them to speak to their own nurseries or childcare facilities to discuss any concerns. Nurseries have rigorous child protection policies in place and will be happy to explain more about these to parents and give information about how they work to ensure children are safe.'
Robin Balbernie, a child psychotherapist who set up and runs an infant mental health service, which works out of children's centres in Gloucestershire, said, 'This is very, very rare. I work with children's centres a lot and if you have adequate staffing, you do think, how can this happen?'
He said, 'If it is physical abuse, with very young children because they can't remember it, it goes into their subconscious. If it is pre-verbal, it can scramble children's attachment - but not always.'
He said this could happen particularly in cases where the abuser is a caregiver, because it impacts on children's trust in adults.
In cases like this, he said, the signs of abuse 'should probably come out very quickly', and 'secure children are more resilient'.
'You look for signs of distress, for example regression in children's development - if children who are potty-trained now need nappies, or if children lose a skill, like language, or if they're clingy, and show signs of emotional upset.'
- See 'A Unique Child: Safeguarding - Take precautions', Nursery World, 2 July 2009.