Two thirds of children aged 14-16 who were cyberbullied during lockdown were targeted through private-messaging apps, according to new research.
DCU anti-bullying researcher has called for a debate on the regulation of private-messaging apps following the finding.
Dr Tijana Milosevic, researcher at the Anti-Bullying Centre in DCU, made the statement after a major study into children's online use during the pandemic.
The research found that almost 66pc of children between 14 and 16 years of age who reported being bullied stated it was more prevalent on private instant-messaging platforms, such as WhatsApp and Viber.
Dr Milosevic said: "I would like to draw attention to the increase in cyberbullying on direct-messaging/instant-messaging apps, which we notice for children who were cyberbullied in the 14- to 16-year age group.
"There's some debate about how to go about regulating such technology, having in mind the private nature of conversations there, which makes these distinct from social media.
"Cyberbullying can look different on private messaging. This can create challenges for prevention and intervention."
Almost a third of young people (28pc) from 10 years old to 18 suffered online bullying during the extended period at home.
Among those cyberbullied, 39pc said this happened more frequently during lockdown; 37pc said it happened about as frequently as before; and 23pc said it happened less frequently.
Cyberbullying was found to be more prevalent within younger age groups, between males, and on private-messaging apps.
Some 42pc of parents reported worrying about cyberbullying and 62pc worried about their children's mental health.
Dr Milosevic said: "We expected to see an increased worry in parents but these findings reveal a number of parents also experience benefits related to digital technology use."
More than half (57pc) of parents reported concern the pandemic would have a negative impact on their child's education (falling behind in schoolwork, failing exams, etc).
The study found 71pc of children and young people reported using their smartphones more during lockdown, as they tried to stay connected to peers. Half of the children also witnessed someone else being bullied.
Fifty-eight percent of parents reported being more worried during lockdown about excessive internet and digital technology use.
The increase in bullying played out as 71pc of children and young people said they used their smartphones more than ever before during lockdown.
Dr Milosevic said: "While we definitely need to be careful about cyberbullying and ensure that every child who experiences it receives adequate help - especially as children's lives become ever more dependent on digital technology - these numbers may not be as alarming as we might have expected them to be."
Only a quarter of parents barred some digital activities more during lockdown and 42pc of parents said they used technology together with their children more.
There was also a sharp increase in children under 13 years old using social media platforms, despite this being prohibited.
Some 75pc of children between 10 and 13 years of age who use social media used it more frequently during lockdown.
More than 1,000 parents and young people aged between 10 and 18 took part in the survey.