UK parents have on average spent an extra £34 on unwarranted app purchases by their children, according to research by Microsoft. 

The problem extends beyond Windows Phone, as iPhone, iPad and Android-owning parents have reported similar issues. The UK's Office of Fair Trading is currently investigating whether free-to-play (aka freemium) games are unlawful, in consideration of the recent outcry over in-app purchases being available to kids.

According to Microsoft's research, over 28 per cent of the 2,000 polled smartphone/tablet-using parents in the UK reported their kids having made an unauthorised app or in-app purchase. Eight out of ten (or 83 per cent) said their monthly bill increased as a result of their child's unauthorised spending. If you have an eight-year-old you might want to keep an even closer eye on him or her, as Microsoft says they're running up the largest app costs of any age group, with an extra £59.59 on average. That's a lot.

Microsoft uses the research to give a plug to its Kids Corner feature that is found within Windows Phone 8. With Kid's Corner, you can decide what your children can open and use, by adding what you want to the section of your phone. Children will only be able to open the apps and other items you choose, and they can also change the name, accent colour and background picture of the Kid's Corner. By default, Microsoft prohibits in-app purchases so your children don't go on a wild spending spree without you knowing. 

As we covered in April, there are ways to turn off in-app purchases for iPhone, iPad and Android as well. On iOS, hit Settings, scroll down to General, and open Restrictions where you can enable a PIN code for in-app purchases specifically. On Android, you can do the same by opening the Google Play store app, tapping on Settings in the Menu, and then by scrolling down to Set or change PIN and hit that option.

News stories have indicated an in-app purchases problem for some unlucky parents. Apple specifically has come under fire, as parents sued in 2011 after receiving big credit card charges raised by kids using their iOS devices. Apple's proposed settlement to the case explains that they will offer a $5 iTunes credit if a child has bought in-game items without a parent's permission or knowledge.

Furthermore, Microsoft says that on average children are spending three hours and 21 minutes a week playing smartphone games and apps.