An extract from “The New Puberty”

What is your most vivid memory of puberty? Is it stuffing tissues in your bra to make your boobs look bigger? Is it a period that arrived unexpectedly and shocked or embarrassed you? Is it looking sideways at the other boys in the class who were taller, bigger and hairier than you and wondering what was wrong with you? Is it people making fun of your growth spurt, or an unwanted erection? Your flat chest? Or do you remember constant anxiety and insecurity about who you were, what you were good at, whether people liked you, what made you special?

I have a vivid memory of realising I had hit puberty – as it turned out, it was when puberty hit me. I was in year 6, so about 11 years old, standing in a crowded tram heading into Melbourne. It was 1984 and I fancy that, in keeping with the times, I may have been sporting a side ponytail. Without warning, the man standing in front of me turned around and accidentally elbowed me in the chest. The pain was terrible, like something hard yet tender and a little bit alien had taken residence in my body, shocking me so much I almost burst into tears. Well, I thought, when I'd regained my composure, this is new. I had no idea what breast buds were, but they had introduced themselves to me in no uncertain terms.

The primary answer to that question is that we're still as awkward as hell when it comes to talking about puberty – to our friends, our parents and particularly to our kids. The education system struggles too. Sexuality education happens on an ad-hoc basis, and flares into controversy more often than is necessary. Governments tread warily, and so do schools. There is a strange cultural reticence behind this – as though talking about those physical changes, and the burgeoning sexuality and reproductive capability they represent, is something shameful and a bit dirty. It's high time we acknowledged how damaging that is and changed our approach, especially in light of what I began to notice over a decade ago.

In the early 2000s, I was a schools reporter – later health reporter – for The Age. One day I found myself at a primary school for a story and, watching the students mill around at lunchtime, something struck me: the senior girls, the year 5s and 6s, were so big. They were tall, they had obvious breasts – they looked like grown women wearing little girls' faces. This seemed to me to be a radical shift from when I had been in grade 6 two decades earlier. Again and again when I went into primary schools, I was struck by how physically developed the kids seemed.

I was not the only one who noticed this change. Media stories started to appear reporting that puberty was happening earlier, and how worrying this was, particularly for the parents of girls. But the focus seemed to be mostly on when girls had their first period, and the evidence was patchy. Some reports included a medical expert saying, somewhat confusingly, that the age of menarche – a girl's first period – had dropped significantly in the past century but had recently plateaued.

At the same time, there were constant stories about the sexualisation of young girls; the aggressive marketing to them of "adult" clothing, make-up and ideas; the sense that they were being pushed out of childhood too soon, for nefarious money-making reasons – with huge psychological and social implications. For boys and girls more generally, there was also the encroachment of social media and the proliferation of all kinds of other entertainment that meant they were being exposed to adult ideas and issues earlier than ever before, that the barriers that had once protected childish innocence were being broken down.

In early 2015, when I returned to The Age from maternity leave, I wrote a story based on the research done by Professor George Patton, head of adolescent health research at Melbourne's Royal Children's Hospital and an international expert on puberty. Having taken a keen interest in adolescent health as a roundsperson, I had worked many times with Patton and his colleague, Professor Susan Sawyer, on a range of issues to do with young people's physical and emotional development.

Patton is overseeing a project called the Childhood to Adolescence Transition Study (CATS). He and his team are investigating exactly when puberty begins, how it unfolds, why children reach it at varying ages and stages, and the impact it has on all facets of children's lives. The researchers are particularly interested in an earlier, and largely unknown, form of puberty known as adrenarche, which happens to children at about eight years of age. They have found that while there are no physical signs of development at this age (which is about year 3), there is a distinct hormonal shift that affects children's emotional wellbeing and their relationships. Boys seem to be particularly affected – a neat reversal of puberty proper, during which, in general, girls are more affected. This means that the entire pubertal process is longer and begins earlier than we thought, and that's even before factoring in that physical development is starting earlier.

Why does this matter? Well, going through puberty earlier is a big deal because it marks, at least from a physical point of view, the end of childhood and the start of adolescence, and the beginning of sexual and reproductive maturity. And because of that, no matter how smooth a kid's puberty might be, it's hard to escape feeling just a little melancholy that it is encroaching further into childhood, a time we like to think of as unselfconscious and free of adult concerns. For girls in particular, physical puberty, or gonadarche, immediately sexualises the body, in a way that is understandably concerning when it strikes young children. It has implications for their physical, social and emotional wellbeing. Much about these complex issues, and the point at which they intersect with puberty, remains a mystery, even to adolescent health experts.

A friend, reflecting on how developed his 12-year-old daughter and her friends suddenly seemed – breasts, acne, the works – summed it up bluntly, but well: "Something's going on." What is that, exactly? One of the best snapshots we have of Australian children and pubertal development comes from the Longitudinal Study of Australian Children (LSAC), a large, long-term study run by a federal government body, the Australian Institute of Family Studies. In an analysis published in 2016, LSAC researchers looked at how more than 12,400 Australian children aged 8-13 were developing, specifically the pubertal changes they were undergoing. One of the most striking findings – although it is important to note that these data are limited because they are parent-reported, rather than scientifically measured – was that almost one in four girls aged 8-9 had started to develop breasts (this included those for whom it had "definitely started" and those for whom it had "barely started").

In fact, by that age, 40 per cent of girls and 21 per cent of boys were showing some sign of the onset of puberty, such as breast buds, skin changes or pubic hair (it is well established that boys generally go through puberty a year later than girls). By age 12-13, almost all girls and about 95 per cent of boys were showing signs of puberty. Interestingly, the age of menarche seemed to align with the figure quoted by medical experts: that on average it happens between the ages of 11 and 13 – 12.5 is the most oft-quoted median age. Although the question was not asked about girls aged 8-9, the data show that by age 10-11, 5.7 per cent of girls had had their first period, and by age 12-13, 57 per cent were menstruating.

Unfortunately, there is no comparable data from, say, 30 years ago to show how this might have changed, certainly not from Australia. But these figures are nonetheless striking. How many of us over the age of about 30 remember girls having breasts in year 3? I doubt I even knew what they were at that age.

I spoke to teachers, parents, doctors and psychologists about all of this. All were worried and perplexed by the changes they were seeing. Prominent child and adolescent psychologist Michael Carr-Gregg told me that, in 30 years of clinical practice, he'd never seen anything like it. He had no doubt that there was a group of kids going through puberty earlier and it was raising a host of issues: shifting relationships, effect on schoolwork, and, importantly, a disparity between the children's physical development and their psychosocial development. It is this disparity that is the main concern – a body that has become an adult's and is perhaps mistakenly viewed as such, attached to a mind that is still a child's.

Adolescence has been a mysteriously neglected area of research. Carr-Gregg said that when he decided to specialise in adolescent psychology in the 1980s his colleagues reacted with horror, telling him he was wasting his time on a group that attracted little research attention. Since then, interest in adolescent health – relating to a specific time of life, with distinctive physiological, psychological and emotional challenges – seems to have gathered pace. But it is still catching up to the understanding we have of other stages of human development.

Governments have invested a great deal of money and other resources in the early years – the vital 0-5 years of pre-school development – matching the understanding that so much of what happens to people later in their lives is set in train when they are very young. And it's entirely right that they do so. But along the way, a little bit of laziness slipped in. Even among the experts there was a feeling that the middle primary years – that seemingly easy period between early childhood and puberty – was a "latent" phase in which nothing much happened. Increasingly, that is being shown to be untrue. The CATS work shows that a big hormonal shift is taking place, and the LSAC data support the idea that puberty proper is encroaching on those primary school years. This means that we need to overcome our reluctance to talk about young children and their development, and take a proactive approach to finding out what is going on, and changing to match it.

The big question is: Why are children experiencing puberty earlier? Again, the reasons are complex and not entirely clear. It is by no means a settled matter within the medical community. There's not a lot of great data on pubertal development, and while many doctors gave an excellent insight into what they are experiencing and treating in their clinical practice, what is happening at the population level is harder to pin down.

One of the points of contestation is whether the earlier signs of puberty that doctors are seeing are part of or separate from puberty. Associate Professor Michelle Jack, a Sydney-based paediatric endocrinologist (hormone specialist), says she is certainly seeing more cases of young girls with premature pubic hair or thelarche (breast development). However, she says this is not early puberty as such, but rather isolated cases of development. Most of those children, Jack says, do not then go through the rest of puberty unusually early. But they do suffer the emotional effects of early puberty, and it can cause the children and their families considerable distress. Similarly, Phil Bergman, head of paediatric endocrinology and diabetes at Monash Health, which services the families of Melbourne's sprawling south-eastern suburbs, also says he is treating more cases of premature thelarche but sees this as separate from actual pubertal development.

Other doctors read what is happening as puberty starting earlier (as in, this is all part of puberty's protracted process). What is clear from all of this is that, given the cultural and social context in which kids are growing up, and the way in which the internet is shaping their lives, a child's path to adulthood is changing and greeting them earlier.

There are a few things we do know. Changes to diet in recent decades is certainly a big factor, more specifically the rise in obesity in children, although the exact nature of the relationship between body fat and earlier onset of puberty has not been established. Some experts also believe that environmental factors play a role, such as the so-called endocrine disruptors, or substances that can change the body's hormonal activity (for example, mimicking the function of oestrogen in the body). The evidence on this also is not yet clear, and the debate around it remains heated, but it is a vital part of determining what is happening to our children and the implications for their health in the long term.

A key reason menarche has dropped significantly in the past century – really since industrialisation – is one of the best possible: our overall health is better. We are better fed now (even if a little too well), and there has been a significant reduction in childhood infections, which can delay puberty. In short, taking into account the problem of obesity, earlier puberty is both a positive and negative indicator of overall health.

But we also need to think about the broader impact on a population of children when a significant cohort reaches puberty earlier. When puberty calls on a group of kids, things will never be the same again. It changes their relationships, including those they have with their bodies, as well as their emotional engagement and awareness of other children's bodies. One of the things we have been very bad at historically is talking to children about puberty – before they go through it, rather than when it is already well under way. We tend to walk them through it in secondary school, or even in upper primary school, when it is too late.

The CATS project, where pubertal changes are reported directly by the children, is instructive on this. Analysing data collected from more than 1000 children aged 11 and 12 (in year 6), it found that by the last year of primary school, fewer than one in 10 girls had not yet started to develop breasts, and only 17 per cent of girls and 27 per cent of boys did not yet have pubic hair. In other words, year 6 is far too late to talk to adolescents about what to expect from puberty: most of them are already deep in it. This is why it's crucial that sexuality education begins much earlier in primary school, to ensure that all children get high-quality, age-appropriate information about what is happening to them, and develop the confidence and resilience to pass through puberty as smoothly as possible.

We are seeing a major shift in the development of children, particularly girls, set within a morphing cultural environment and a technological revolution. These changes are complex and vitally important, and we cannot afford to ignore them and hope they will go away. Hysteria is not helpful either. This is not the "end" of childhood but the reconfiguring of it. It has huge implications for how we teach and raise our children, and offers a rare opportunity to overcome our prudishness about talking about puberty.

My friend was right. Something is happening to our kids, and it's time we talked about it.

This is an edited extract from The New Puberty.