A report by Childwise says kids are now online for three hours a day on average each day, compared to around two hours in front of the box.
Speaking on Premier Christian Radio's New Hour programme Matt Pearman, a youthworker at the Newquay Christian Centre in Redruth, said: "The amount of stuff that young people and children can access on the internet is just so varied.
"I think, as young people start to watch more and more, they actually, potentially, can become desensitised to stuff and their view on reality is distorted.
"We've seen young people in our youth group, for example, [when] an argument will start online because they can say whatever they like and they don't physically see that person.
"It makes me question whether, if they could see the other the other person they're speaking to and they could see the emotion that they're feeling, whether they would actually write those things they're writing or look at the things they're looking at."
YouTube, Instagram, Snapchat and Facebook were apparently among the websites most visited by children, while Childwise's survey also found more five to 16-years-old watched programmes on Netflix than ITV or BBC One.
The number of children who own a tablet rose by 50% in the last year.
Simon Leggett, Childwise research director, said this year's survey showed that "TV viewing has been redefined".
He told the BBC: "Growing access to the internet at any time and in any place, and a blurring of television content across channels and devices, brings a landmark change in behaviour this year.
"Children are now seeking out the content of their choice. They still find traditional TV programmes engaging but are increasingly watching them online and on-demand or binge-watching box sets."
Matt Pearman added: "I do believe we've got a role to play in this, in guiding the young people...
"I was thinking about food and a child. You wouldn't just stick a load of food with junk food and great food in the basket and say "Here, help yourself" and I think it's the same with the internet.
"We have a responsibility to guide young people to what's safe and healthy for them on the internet and how much they use it as well."