Thunberg was variously infantilised, her appearance and intellect mocked or questioned, she was patronised and her credibility and mental health debated. But her resolve was stronger than her critics and she took the disparagement as an opportunity to highlight the need for diversity and difference in public and political life.

Today we celebrate International Day of the Girl Child. Girls' rights charity Plan International Australia has launched new research revealing girls and young women see sexism as the biggest issue facing them (62 per cent), but they also feel that they are well placed to combat it and to achieve gender equality.

They are influenced by strong female leaders and activists, ranging from Jacinda Ardern and Julia Gillard to girls closer to their age: Greta, Malala Yousafzai and Emma Watson.

We need young women's and girls' voices. We need them engaged in leadership and decision-making. This is the only way to achieve prosperity for all. When I became a senator, I loved receiving letters from young women saying if I could do it so could they.

But I find it incomprehensible that, in the almost 24 years since I first set foot in Parliament, when the numbers were around 15 per cent female, the number of women in the ranks would merely double. We now have a record number of women in the federal Parliament yet it's just a third.

At 26, I was a young, single woman, with a part-Croatian surname and had to deal with the novelty and ridiculous stereotypes that came with it. I was subject to relentless references to age and appearance, being told what to wear, enquiries about personal life and headlines focusing on blonde hair. When I was married, one newspaper put a journo on pregnancy watch. At my first business lunch, I was asked if I went into politics to meet a husband (of course not).

Almost a quarter of a century later, I did not anticipate that today women would still confront outdated stereotypes, double standards in the media or debates about their parental or marital status, let alone comment about their appearance or starting a family, when it came to their suitability for politics.

The inherent value judgment in commentary around women in politics remains. When NSW Premier Gladys Berejiklian was elected, a columnist wrote she "lacks a spouse and children" and when New Zealand PM Jacinda Ardern announced her pregnancy, she faced demeaning questions.

As a relatively young senator, I was excited to take my place in the Senate and took seriously my role in encouraging women - of all backgrounds and ages - to get involved in politics. My favourite and most empowering times in the Parliament were when women across the political spectrum worked together to bring about change that benefited women and girls (and the broader community) on issues such as stem cells, transparency in pregnancy counselling and the removal of RU486 from ministerial discretion.

I knew legislation could change lives for the better and understood that power was important for women and that people with power don't share it or relinquish it easily. I learnt how uncomfortable some people were with women having power, especially young women.

In recent weeks, we have seen just how uneasy some still are with the idea of a girl leading a political movement. But having vibrant women in public life is not enough by itself. Sustained support for the world's young women - through advocacy, education and mentoring, and through practical support to address the many barriers to their progress - is crucial.

Australian young women and girls are tuned into the big issues. They know that the key issues preventing girls around the world from achieving their dreams are sexism, violence, discrimination and lack of education and opportunities to lead.

Overwhelmingly, girls want to lead social change, but don't necessarily feel they are being heard. The statistics remind us of the magnitude of the challenges they face. We live in a world in which, every three seconds, a girl is forced or coerced into marriage.

Worldwide, nearly 50 per cent of all sexual assaults are against girls aged 15 years or younger. The leading cause of death for young women aged 15 to 19 living in developing countries is pregnancy. It's a world in which at least 65 million girls are out of school and a girl in South Sudan is more likely to die in childbirth than she is to finish primary school. Education brings power, it brings change, it gives people a voice and agency, and it creates sustainable development.

Sustainable change can never be achieved until girls are able to live free of discrimination and free of violence and the fear of violence. So, alongside work to encourage young women's leadership, we must also create safe environments for them to realise their potential.