London - Like many parents, Debby Penton allows her sons, Ben, 13, and Luke, ten, to play computer games — with much reluctance and strict time limits.
She also researches less violent options, so when one afternoon she heard Ben shouting at the television, she was concerned. Watching him gesticulating and snapping at the friend who was playing with him, she could instantly sense that Ben’s immersion in the game was too intense.
Debby, 45, from Surrey, says: "I noticed how, eyes glued to the screen, brow furrowed, he was really living the game — it was disturbing to watch. Then there was all the shouting and arguing which just isn’t like him. I unplugged it and he became so frustrated that I banned all electronics for a week."
Welcome to Fortnite, the PlayStation, computer and XBox game which has taken the world by storm. With more than 40 million players globally, connected to each other via the internet, there are thousands of schoolkids glued to it.
If you have children aged around ten, you will no doubt have heard the name. And perhaps, like Debby, you are starting to see a darker side to this seemingly innocuous game.
For the uninitiated, Fortnite: Battle Royale is an interactive game of survival where players create a superhero avatar and compete against each other on a dystopian island. Each game, or "match" as each competition is known, starts with 100 players.
Inspired by the Hunger Games novels and films, children can play solo or team up with a friend - or a group of friends - to compete as a duo or squad, which adds a social element to the game and players can chat as they roam the island using headsets and microphones.
Hidden around the island are weapons including crossbows, rifles and grenade launchers, and players must arm themselves as they explore.
The last survivors are the winners.
Many parents were initially taken in by the cartoon-like graphics and seeming lack of bloodshed, believing it to be relatively child-friendly. All the same, if your character is shot, it crawls on the floor clutching its wounds, so there is certainly a macabre feel to it.
And some experts say that the fact no blood is shown may even desensitise young, impressionable players to the impact of such mindless violence.
These days parents are all too aware of the dangers of too much gaming - sleep issues, obesity and difficulty interacting with others. But the major concern with Fortnite is its apparently addictive nature, and the way it can affect a child’s behaviour.
Ordinarily pleasant children are having furious tantrums or aggressive arguments when asked to stop playing. Some even demonstrate depressive behaviour. It is a creeping concern permeating many middle-class homes. A report on morning television a couple of weeks ago spoke to a mother saying that she felt she had lost her son to the game.
"What you have to remember is that the metric for any online game, or indeed social media platform, is the 'time spent' on it," says Dr Linda Papadopoulos, psychologist and Internet Matters Ambassador.
"As such, these games are designed to make it hard to stop playing. Behavioural scientists are employed to ensure that the brain’s reward system is manipulated so that kids feel so excited and engaged that they just can’t stop playing. Do you really think a 12-year-old is going to win against a Silicon Valley-employed behavioural scientist?"
And as such it’s more difficult for parents to impose time limits: "Companies know parents limit screen time," says Dr Papadopoulos. "They need to make their game the most compulsive, so that when kids are allowed to play, it’s their game which is chosen." She says it’s irrelevant that the game is ‘age appropriate".
"It still has the potential to become compulsive, so parents need to be on top of it, looking out for changes in kids’ behaviour, and balance how much game time they engage in with other social, physical, family and peers’ activities."