More than a third of eight to 13-year-olds rarely or never talk to their parents about online safety, a survey has found.
Of this group, a third said they are in regular contact with a stranger online.
The survey of 1,500 children was carried out between September and November by CyberSafeIreland, a charity that educates children and parents about web safety.
Released to mark Safer Internet Day today, it found more than two-thirds of children own a smartphone, a quarter spend two hours a day online and two-thirds use social media.
A third of those surveyed said they rarely or never speak to their parents about online safety, which the organisation said leaves these children particularly vulnerable.
Within that group, a third are in regular contact with strangers online and half use social media platforms that are not supposed to be used by under-13s.
CyberSafeIreland has said the findings show young children in Ireland are putting themselves at risk online and has called for a national campaign to support parents and teachers.
Chief executive of CyberSafeIreland Alex Cooney said: "Children are exposed to a variety of risks online, as has been highlighted in recent press coverage surrounding some very disturbing cases.
"It is essential that any child who has access to the internet, especially when they are young, only does so with guidance and supervision from a parent or carer.
"We urgently need a National Parents Campaign, much like we have had over the years for road safety and healthy eating, to provide guidance and support to parents and to create social norms around safe online use."
CyberSafeIreland is also urging parents to play a bigger role in their children's online lives by starting a conversation with them, doing their research and setting rules.
While it has expressed concern that there may not be sufficient advice available for parents, CyberSafeIreland is nonetheless urging them to try to find out more.
It has also produced a leaflet for parents, supported by Tusla, which has been sent to all primary schools.
Safer Internet Day marked
Meanwhile, Webwise - working with An Garda Síochána - launched a new educational resource to mark Safer Internet Day.
"Be In Ctrl" has three lessons, an information pack for school leaders, a campaign video and is supported by a garda schools talk.
The resource, designed for Junior Cycle SPHE, will be free to order or download from today.
Elsewhere, students from eight schools around Ireland will today receive awards for their winning entries into a poster competition aimed at stopping online bullying.
Run by the National Anti-Bullying Research and Resource Centre at DCU and Facebook, the TackleBullying.ie competition was aimed at raising awareness of the anti-bullying website developed by the centre.
More than 250 entries were received, with 11 winners chosen.
Meanwhile, also to mark Safer Internet Day, cybersecurity company TrendMicro has launched its seventh annual youth internet safety video competition.
This year the theme is "How do you know who and what to trust online?"
The competition aims to highlight the increasingly toxic issue of misinformation, disinformation, online hoaxes and scams.