You have nobody to blame but yourself.

Which is why Apple settled their class action on this subject, and as a direct result altered the appstore to mark free apps with IAP as such.

I don't enforce parental controls (restrictions). They are too old for that crap.

However I don't want adverts in web pages that have detected an iPad forever redirecting to the app store. Then when you switch back to safari they reload and back to the app store app again unless you are quick.

It's like the bad old days of the Internet again playing banner whack a mole.

I think you misunderstood the OP. The problem is not that his kids bought things behind his back.

Gotta' read reviews before you buy anything on the app store.

On them, not by them.