I tell ya, I wouldn't have said anything to anybody.
According to the article, the boy bought a video game console and two games were supposed to come with it. There was a load of cash instead. The parents called the police. The kid may get to keep the money if the "owner" is not found.
Would I have kept the money? £44,000 is nothing to sneer at. No, I think after the initial shock of finding the money and spending it in your head, you'd realize that someone knows where this money was delivered to. They have your address. They may come looking for the money. That's probably why it was stashed in there.
Scary, actually. This could make one hell of a good book, a thriller. Maybe this is the catalyst that I need...