The Office of Fair Trading is investigating iOS Apps and other web and phone games that are aimed at children over in-app purchases and hidden extras that have lead some children to ramp up huge bills for their parents.

In the US, Apple is already paying out £66 million in compensation for parents whose children racked up large bills through in-app purchases while using free-to-download apps.

The OFT will investigate these games are putting "misleading, commercially aggressive or otherwise unfair" pressure on children to pay for additional content, according to a BBC report.

"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," OFT senior director Cavendish Elithorn told the BBC.

In many of these games players are encouraged to purchase coins and other virtual items in order to perform well in the game. The OFT maintains that the game developers are breaking fair trading laws if they are applying pressure on the game players.

The vast majority of mobile games are free to purchase but offer expensive in app purchases. In one case identified by the OFT in-app purchases were as high as £70.

A number of cases have come to light recently where children have run up large bills. One five-year-old from Bristol spent £1,700 on the Zombies versus Ninjas game. This money was later refunded by Apple. In another case a father sued after his son spent £3,700 on an App Store game Plants vs Zombies and NOVA 3. An eight-year-old boy racked up a bill of almost £1000 while playing a Simpsons game.

Following the recent bout of incidences that saw parents faced with huge iTunes bills after their kids had unwittingly downloaded in-app purchases, Apple has highlighted its "Parents' Guide to iTunes" section in the UK App Store's Featured tab.

The "Parents' Guide to iTunes" offers advice about Apple ID Passwords, limiting the amount children can spend through the use of Gift Cards, the Parental Controls available on iOS devices, and device Passcodes to stop children from being able to access the iPad or iPhone at all.

Additionally, Apple has also introduced a disclosure to apps in its App Store, to alert customers to the fact that the app has in-app purchases.

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