More than 80 per cent of nine to 16-year-olds are said to be using the internet for gaming.

And online gaming isn’t without its pitfalls. In the past month there have been reports of children as young as five and six running up iPad bills – the greatest amount was £2,000 – after innocently downloading apps for so called “free” web and app-based games.

Now the Office of Fair Trading has stepped in to investigate whether children are being unfairly pressured or encouraged to pay for content in free games, such as upgraded membership or virtual currency in forms including coins, gems or fruit.

Typically, players can access only certain areas of these games for free and must pay for higher levels or features. The OFT has written to companies providing such games requesting information on how they market to children, and is asking parents and consumer groups for information about potentially misleading or commercially-aggressive practices.

The OFT’s investigations will look into whether these games include “direct exhortations” to children, or strong encouragement to make a purchase, to do something that will require making a purchase, or to persuade their parents or other adults to make a purchase for them.

It will also consider whether the full cost of some of these games is made clear when they are downloaded or accessed.

Cavendish Elithorn, OFT senior director for goods and consumer, said: “We are concerned that children and their parents could be subject to unfair pressure to purchase when they are playing games they thought were free, but which can actually run up substantial costs. The OFT is not seeking to ban in-game purchases, but the games industry must ensure it is complying with relevant regulations so that children are protected.”

David Lodge, divisional manager of West Yorkshire Trading Standards Service, welcomed the OFT’s moves.

He added: “In the meantime, parents need to be aware that if their children have access to online facilities including games they need to be extra vigilant in monitoring what services they are accessing.”

Kelly Quirke, a parent and nursery nurse at Daisy Chain Nursery in Allerton, allows her son Hayden to play educational games under her supervision.

“I have a lock on my iPad so he can’t access any games unless I am with him,” she says.

Kelly welcomes the OFT’s intervention. “I would not be very happy if I went on to my bill and it was hundreds of pounds because my son had played on games,” she says.

Siobhan Freegard, founder of parenting website Netmums. com, says: “There’s no such thing as a free lunch, and there’s no such thing as a free app either – despite how they’re marketed.

“We have heard of cases where parents have been hit with bills for hundreds of pounds as the apps are linked to their card details through iTunes. Often the bills aren’t immediate and it takes days to find out they have been charged.

“Few people mind a couple of targeted ads which are relevant to the app service, as they realise it’s the price to pay for the ‘free’ app. But bombarding children using so-called free apps with expensive products and services they can unwittingly sign up to with a couple of clicks is immoral.

“App makers should be made to follow a code of conduct and have a rating system which shows as soon as the app opens. There must be a clear, easy and immediate way for parents to switch off purchases.”

Ken Corish, from the UK Safer Internet Centre, said: “In the online safeguarding education we run for parents, the issue of in-app purchases is one parents frequently raise and one with which they feel disempowered to deal with, either because the technology gets in the way or their child may know more than them. While there is an onus on industry to consider its target audience, the best step parents can take is getting involved in the choices their children make about choosing games.”

He says the website common sensemedia.org provides an online information resource for every game, app, book or film available with clear information about content, learning potential and suitability.