Children are increasingly using social media to promote activist causes, in what has been dubbed the "Greta effect".
Last year saw an increase in the proportion of 12- to 15-year-olds who use "social media to support causes and organisations by sharing and commenting on posts", watchdog Ofcom reported.
This is thought to have been inspired by Swedish climate change activist Greta Thunberg, 17, who has travelled across the globe urging world leaders and big business to do more to tackle climate change.
In 2019, nearly a fifth (18 per cent) of 12- to 15-year-olds in the UK used social media to express support for causes and organisations that may be environmental, charitable or political - up from 12 per cent in 2018.
Ofcom also found that one in 10 children in the age category signed an online petition in the last year.
Despite an upturn in youngsters using social media to promote causes, parents have become increasingly concerned about their children's activity on social media and online.
Ofcom found that 55 per cent of parents and carers believe that the benefits of youngsters being online outweigh the risks - a 10% decrease since 2015, according to the watchdog.
This has coincided with more children seeing hateful content online than they were previously, with 51 per cent of young people seeing such material in the last year.
This is an increase from 34 per cent in 2016.
- Video report by ITV News Consumer Editor Chris Choi
Yih-Choung Teh, strategy and research group director at Ofcom, said: "Today's children have never known life without the internet, but two million parents now feel the internet causes them more harm than good."
Research found Facebook, Snapchat, Instagram and WhatsApp ranked as the most popular social media websites.
Around half of all children aged 10 own their own smartphone.
The Ofcom report, Children And Parents: Media Use And Attitudes Report 2019, was based on interviews with around 3,500 parents and children.