I will never forget the first time I visited a women's prison. I was 23 and had been working as a volunteer researcher. Tasked to ascertain women's concerns about their release and resettlement, I couldn't wait to hear directly from those women I had been seeking to represent. In hindsight, nothing could have prepared me for the sense of despair and pain that permeated so many of the conversations I had that day. So many of those I spoke to had lost their children and their homes, and their priority on release was to get both back. At the time, there were calls to reduce the number of women in prison for non-violent offences and to reserve the use of custody for public protection and as a last resort.

So a huge wave of frustration came over me when I read this month's report, published by the Criminal Justice Alliance, highlighting that the total number of women in prison has trebled over the past two decades to around 4,000.

This increase is not simply due to a rise in women's use of violence. While about 100 more women a year are serving short custodial sentences for violence, the most common offences are theft and handling, and breach of a community order. And many will be imprisoned on remand. It is clear that while attempts have been made to challenge the numbers of women in prison, through the work of organisations such as the Prison Reform Trust and Women in Prison, the use of custody by magistrates remains a concern.

Whenever the debate about women in prison resurfaces, so too does the concern that women should not be treated better simply because they are women. But gender neutral policies in criminal justice do not have gender neutral consequences. Every year, 18,000 children see their mothers go to prison, and only 5% of those children stay in their homes during that sentence. A third of women in prison are lone parents, and it is more likely that their children will lose their homes or be placed in care.

Figures published by the Prison Reform Trust last year illustrated that although women made up only 5% of the prison population in 2009 they accounted for 43% of self-harm incidents, and women in prison are five times more likely to have mental health problems than the general population.

The life histories that women in prison have recounted ? domestic abuse, childhood abuse, drug and alcohol dependency and the resulting mental health problems they face ? need greater attention. Little consideration is given to the many support services that women may be dependent on to prevent their offending or reoffending.

When a child loses their home and their sole carer because their mother is in prison on remand or has breached a community order, for example, who are we seeking to protect? And who are we punishing? Rather than dismiss these questions for fear of "letting women off the hook" we need a more considered debate about the purpose of prison, and who its use affects.

Simply pointing the finger of blame at magistrates will not suffice, and fails to recognise the wider context within which sentencing decisions are made. An approach that identifies the importance of preventive and support services for women is required. When the debate starts and ends with the decision of a magistrate, it has begun too late.

? Carlene Firmin is a principal policy adviser at the Office of the Children's Commissioner for England. She is writing in a personal capacity