With the launch of Angry Birds 2 this week, parents are being warned to make sure they keep control of in-app purchases.
Like many games, it allows players to pay real money for certain short-cuts. If users fail five times to complete a level in a certain period of time, they are forced to wait before trying again - unless they fork out for 'gems'.
And according to a survey from price comparison site money.co.uk, almost a third of 5-16-year-olds have been in trouble with their parents for racking up a bill online using their parents' payment accounts.
And while some spent as much as £600 a year, over half were unaware they were doing it. Of these, almost half were gaming and didn't realise they'd made virtual purchases, with more than a third unaware that payment details were saved on the device.
"Whilst gamers delight in the arrival of the latest version of our feathered friends in the form of Angry Birds 2, the new format should come with a slight health warning for unsuspecting parents," says Money.co.uk editor in chief Hannah Maundrell.
"With 8.7 million 5-16 year olds on school summer holidays at the moment, this well-timed launch lands in peak season for children racking up bills on their parent's online payment accounts."
Many parents don't even realise it's happening, with 3% saying they don't check their statements. And just 10% of those who have been hit say they managed to get the money back from the credit card provider involved, and only 9% got a refund from the actual seller.
Angry Birds maker Rovio defends the availability of the in-app purchases.
"With Angry Birds 2, we obviously put a lot of time and effort into making it feel fair - that you feel justified in spending money, that you get your value - from that spend," creative director Patrick Liu tells the BBC.
"We have no interest in tricking or exploiting our fans. And I think it's fair, because you can access the whole game without spending anything."
Parents wanting peace of mind are advised to keep their children out of temptation.
"It's worth blocking in-app purchases and setting up parental controls on any device your child uses," says Maundrell. "Equally, disabling pre-populated payment details and staying aware of what they're doing online should help protect both of you."
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