A new study has found that 40% of children in secondary school faced cyberbullying during the last school year.
The survey by CyberSafeKids found that over 25% of primary school aged children also experienced harassment online, with girls more likely to be victimised than boys.
Almost two-thirds of teachers said they had dealt with online safety incidents.
The survey found that 93% of eight to 12 year-olds have their own smart device, with YouTube (76%) the most popular app, followed by WhatsApp (39%), Tik Tok (37%) and Snapchat (37%).
Online gaming is also popular with young children, with 15% playing over-18 games like Call of Duty and Grand Theft Auto.
Almost three-quarters of 12-16 year-olds said they can go online whenever they want, with 40% posting videos of themselves on social media platforms.
Younger children face more controls at home from parents, but 31% of eight to 12 year-olds said they are free to go online whenever they want, and 15% of primary school children have no rules in place for going online at home.
Posting pictures without permission, creation of fake profiles, and being excluded from chat groups were among the commonly reported forms of cyberbullying behaviour.
The research found that only 52% of primary school children, and 39% of secondary school children, told a parent or trusted adult they were being bullied.
Between one-quarter to one-third of children - 28% of younger children and 34% of older children - didn't tell anyone.
Some 42% of young boys and 27% of girls have gamed with a stranger online.
Young children are also unaware of how best to protect themselves online with 22% posting videos, and 17% unaware of how to manage privacy settings.
Over one-quarter of all the children surveyed had seen or experienced something online in the last year that "bothered" them, such as sexual or violent content.
Nearly half of the younger children didn't tell a parent or trusted adult about this experience, rising to 67% for secondary school children.
'Not enough is being done'
CyberSafeKids CEO Alex Cooney said the issue is not being taken seriously enough.
"Online safety for children remains a critical issue that is not being sufficiently addressed in Ireland’s education system or by the social media companies whose platforms are being used," she said.
"Our data shows children are extremely active on social media, often unsupervised, leaving them highly vulnerable to bullying, grooming, and exposure to violent or sexual content.
"We've been reporting on these patterns for the past seven years, but not enough is being done.
"We urge the Government to invest heavily in more resources and campaigns to support both parents and educators.
"Whilst organisations like CyberSafeKids barely have the funding to survive, many online service providers report annual profits in the billions," she added.
CyberSafeKids surveyed over 5,000 eight to 16 year-olds between September 2022 and June 2023.