Now if you are in the same situation as me and have equipped your kids with Android devices then Google Play Store (a.k.a. Market) provides some "User Controls" options. You can setup content filtering and protect the settings with a PIN code. You can also choose that the PIN code must be used to be able to purchase apps. Very useful because after all it is your credit card that is tied to Google Checkout because they are kids and kids do not have credit cards, at least not where I live.
To be able to change the settings you've setup you need to push "Unlock settings"...
... and enter the PIN code that only you know.
All good so far. This is secure, right? In December last year I started to wonder just what would happen if I cleared the data for Market (it wasn't renamed to Google Play back then) and I gave it a try. Well what happened is that on the next start of Market it started up fresh as expected but what I did not expect was that also the "User Controls" options, including the PIN code, was reset.
So I decided to try to report this bug to Google and found that someone allready had done so and I added my comments to the bug report and starred the issue.
Now 4 and a half month later with several new versions of Market and later renamed to Google Play Store the bug is still present. I just tried with Google Play Store 3.5.16 and all you need to do is push a button...
...and all the protection is gone.
And no, this does not require a rooted device.
If you, like me, think that this bug needs to be fixed then "star" this issue in order to bring Googles attention to it: http://code.google.com/p/android/issues/detail?id=20702