The facts of the Plymouth case challenge our understanding of human nature. Not simply the idea that people can find pleasure in the sexual abuse of very young children. But the revelation that women were involved.

But, as I have reported here before, child abuse is far more commonplace than most people comprehend and there are an increasing number of studies suggesting the involvement of women is significantly under-reported.

According to research by the National Centre on Child Abuse and Neglect in the United States, the sexual abuse of children by women "constituted 25% (approximately 36,000 children) of the sexually abused victims" in their study. "This statistic is thought to be underestimated due to the tendency of non-disclosure by victims", the report goes on.

In the UK, Childline says that 11% of the calls received from children alleging sexual abuse suggest the perpetrator is a woman.

The NSPCC says that women are the abusers in 6% of cases highlighted in their study.

However, all these estimates - from the last few years - are far higher than had previously been acknowledged.

Michele Elliott, founder of the children's charity Kidscape and author of the book Female Sexual Abuse of Children: The Ultimate Taboo put it this way today:

"Women abuse children for the same reason men abuse children - for sexual gratification, for power. Quite frankly it is something they enjoy doing. I know that is hard for the rest of us to comprehend but women are no different than men in that case."

In June this year, the Australian child welfare charity Child Wise began a television advertising campaign highlighting the risks from sexual abuse by people entrusted with the care of children. You can see the latest ad here.

Child Wise has calculated that almost a third of sex abuse by women takes place in an organisational setting, notably kindergartens and baby-sitting. The majority of such abusers are not coerced by a man but initiate the abuse themselves. The damage can last a lifetime.

Police in Britain fear that new technology has made all forms of child abuse easier and more commonplace.

As in today's case, the internet allows paedophiles to communicate and share child pornography. Mobile phone cameras mean images can be shot and disseminated around the world within seconds.

A kindergarten close to the Plymouth nursery involved in today's case is banning mobiles with cameras on its premises. But risk can never be eliminated.

Background checks on staff won't spot those who have never abused before. The new vetting scheme currently being rolled out across England, Wales and Northern Ireland would not have helped in this case.

But there is another danger too. That we allow fears about paedophilia to damage the relationship between adults and children and to undermine the trust that makes communities function.

