One in two teenagers here has watched or read sexually explicit materials, a poll has found, with some as young as seven when they were first exposed to it.
And one in three admitted viewing pornography in the past year, whether intentional or accidental.
The first large-scale survey here to examine children's exposure to pornography, which polled 836 students aged 13 to 15, was conducted by Touch Cyber Wellness, the main agency that gives online safety talks in schools here.
Experts say the findings are worrying as such content affects young people's attitudes and behaviour towards love and sex, and may lead to sexual crimes.
Dr Munidasa Winslow, an addictions specialist in private practice, called the figures "expectedly horrendous".
"Technology is driving a new wave of addictions - whether gaming or pornography - because... now, it is all available at a click," he said.
In the survey, 77 per cent of those exposed to sexual content accessed it through smartphones.
The findings largely echoed those elsewhere. Studies in the United States and Australia found that about 40 per cent of teens and pre-teens visited X-rated sites deliberately or accidentally.
In the Touch survey, 5 per cent of the teens who had seen porn encountered it first in lower primary levels - at age nine or younger. They were not asked how often they accessed this subsequently. Pornography was defined in the study as images or content, such as anime and erotic novels, that depicted naked people or people having sex.
Students from three secondary schools were polled, and 24 were interviewed in depth one on one.
Experts say the results reflected how Singapore has one of the highest rates of mobile phone use, and insufficient adult guidance.
"I believe it is largely due to the inadequate discussions and lack of guidance from parents, so young people look elsewhere for sex education, of which pornography is a poor teacher," said clinical psychologist Joel Yang of SIM University.
Based on the interviews, many boys started viewing sexual content out of boredom or curiosity, said Touch Cyber Wellness assistant manager Chong Ee Jay.
Asked how they first encountered such materials, half the boys polled said they deliberately sought these online. A third of the girls read these in erotic or romance novels. The rest came upon these by accident or were egged on by friends.
Experts say the effects of viewing porn may vary by gender.
"It may lead to pressure on girls to look and act a certain way when they compare their bodies with those online. When boys see the male figures as aggressors or in positions of dominance, they may become disrespectful towards women," said Mr Chong.
The obsession with porn affects their studies, self-esteem and interpersonal relationships. Overseas studies have also shown a link between consuming pornography and committing sex crimes.
Since adult-only materials are readily available, experts say parents should install Web filters on computers and mobile devices. They should also tell their children that porn is not sex education, and where to seek help.
Sex education teachers should not shy away from the topic either. Mr Chong will be training them on how to broach the topic.
Dr Winslow said: "For sexual addictions, people are only as sick as their secrets. The more they can talk about them in safe places, the more the addictions lose their hold or power over people."
Ms Yap Chai Kian, 43, a manager with a nine-year-old daughter and a 13-year-old son, said she has been having regular conversations about sex and porn with her children since they were two.
"I try to find opportunities to talk to them, like when crime shows on TV show people sending sexual images to one another, so that it does not feel awkward."