It happened very quickly and very easily.

Their computer at home has a filter on it, but they were visiting a friends' house and Mia was loaned an iPad that was not set up for children.

Sarah put Mia on the ABC Kids website but before long, realised her daughter had strayed into unfamiliar and scary territory.

Prompted by other kids boasting at school about "cartoon sex", Mia had typed the search terms into Google and was bombarded with explicit images and videos, one of which showed a character in chains.

Mia was worried she might be in trouble. Sarah was worried about whether Mia was upset by what she saw.

"I remember thinking: 'Oh God'," Sarah says.

"I wondered how her head processed that. It looked like torture."

Sarah is far from alone when it comes to raising a child in an age when pornography is just a few clicks away.

Gone are the days when kids' exposure to explicit material involved a cheeky peek at an older sibling's Playboy collection. Or a curious perusal of a parental copy of the Joy of Sex.

Pornography is available in abundance on the internet. And the internet is everywhere, meaning young children and teenagers are easily able to access free, hardcore content if they want to - and even if they don't.

According to research released by the Office of the Children's eSafety Commissioner in February, Australian teenagers are going online more often, on a broader range of devices and with increased use late at night. For example, in 2011 less than a quarter of teenagers used a smartphone, as of June 2015, 80 per cent did.

Even a few years ago, a child's access to the internet would have been limited to the home desktop, now they may have access through phones, tablets and laptops. And if they don't have access, their friends do. As the Australian Medical Association notes: "It is now a reality that children and young people are increasingly coming into contact with internet content designed for adults."

The 2011 AU Kids Online Study found that of the 9-16 year-olds surveyed, 44 per cent said they had seen sexual images in the past 12 months. Almost 30 per cent said they had seen sexual images online. Younger children were less likely to have seen images on the internet, with 11 per cent of 9-10 year-olds reporting they had seen sexual images online, compared to 56 per cent of 15-16 year-olds.

This comes amid general concerns about the trend towards more violent and misogynist pornography and its continued lack of condom use. As US anti-porn activist Gail Dines writes in her book Pornland: "Images have now become so extreme that what used to be considered hardcore is now mainstream pornography.

"Youth today, especially boys, are catapulted into a never-ending universe of ravaged anuses, distended vaginas, and semen-smeared faces."

Late last year, a multi-party group of conservative Senators launched a parliamentary inquiry into the issue. At the time, former Labor senator Joe Bullock (who quit Parliament in March), told the Senate: "Exposure to pornography has measurable negative effects of brain development and behavioural outcomes."

The inquiry has since been inundated with submissions from teachers, doctors, researchers and voters expressing serious concerns.

The Association of Heads of Independent Schools of Australia said teachers were overwhelmingly reporting that young people were being prematurely sexualised. The AMA said that there is a "strong link" between online porn and risky behaviour in adolescence. This includes "earlier and more diverse sexual practice that can result in adverse sexual and mental health outcomes".

Victorian sex educator Margaret Buttriss reported that she had spoken to children as young as four who had seen pornography by accident, while child protection expert Freda Briggs warned that children can become addicted to pornography and "rape younger children".

But other experts have cautioned that more research is needed before definitive conclusions can be drawn.

The Royal Australasian College of Physicians has stressed that studies are needed on the kinds of porn Australian children and teenagers are accessing and how this is affecting their social and romantic relationships.

The Melbourne-based Burnet Institute says that while pornography use is "associated" with some harms - particularly when people watch violent porn and watch it regularly - there is "little evidence" to say it causes harms in adolescents and young adults.

It also notes there is "very little robust research internationally or in Australia" that look at pornography's use and harms among children.

One thing that experts do agree on, however, is that when it comes to young people's exposure to pornography, it is a case of "when" not "if".

"You can't hide from this," Children's eSafety Commissioner, Alastair MacGibbon says.

"The simple reality is, a child - either by accident or design - will gain access to this type of material."

While there are pushes for increased filtering of the internet, MacGibbon says this is not the silver-bullet solution. Filters can be effective when installed on home and school systems for smaller children, but older children can usually get around them.

Overwhelmingly, the Senate inquiry has heard of the need for more educational support to help young people deal with what they may encounter online.

MacGibbon notes that many of the parents he talks to feel helpless or "disempowered" when it comes to their children's internet use. Kids are notoriously ahead of their parents when it comes to technology know-how.

However, he stresses parents can (and should) make a difference. Some of this simply involves asking their children to tell them about the apps and devices they use - and to teach them how to use them. For younger children, it is also possible to "watch over their shoulder" when they are online.

But a large part also comes down to parents talking to their kids about sex, porn, relationships and ethics.

"While these conversations are tough, if you don't have them, [kids] are going to be finding out about this stuff without your guidance and love and advice," he says.

MacGibbon also notes it needs to be done "earlier than people think", adding the need for this to be in an age-appropriate fashion.

For example, while a conversation with a teenager might centre around how pornography does not depict "real" sex, the message to a younger child might be "if you see something you don't understand or makes you scared, or uncomfortable, come and chat to me".

Wollongong University associate professor Michael Flood - whose research includes pornography and male sexuality - adds there is an important safety element to talking to children early on.

"Maintaining children's sexual ignorance fosters sexual abuse," he says.

"Young people who know their sexual rights and responsibilities are more likely to speak up when they are being forced into sex, and they are less likely to abuse others."

Macquarie University's Catharine Lumby, has recently interviewed 13-17 year olds about where they get their information from about sex, as part of an Australian Research Council grant. The focus groups revealed only about 20 per cent of teenagers would talk to their parents about sex.

"That is really frightening to me," the professor of media says.

"That means it's all left to the school."

While Lumby is concerned about the potential harm being done to kids, she also notes that the online world presents opportunities as well as risks.

None of the age groups she interviewed reported being "significantly disturbed" by the explicit content they saw online. Both girls and boys groups also talked about finding "useful material" in their internet travels, acknowledging there was a lot they did not know about intimate relationships.

"What they are looking for is support."