I don't think you understand how this works. It happened to me, so I know.
I have an IPad. I have purchased many apps, and each time it asks me for a password. I let my 7-year old daughter use the IPad, confident that she could not purchase anything because she did not know my password. I downloaded a game for her, one that her friend had told her about, called Tap Zoo. The game was free; I put in my password to download the game, and then gave her the IPad so that she could play. Later that night I got an invoice from Apple for "gems" and other things to the tune of $200.
She did not enter any passwords. She thought that she was using game money to purchase these items. It turns out that Apple cached my password for 15 minutes, and that allowed her to make real dollar purchases without entering a password. I had never heard of the setting to "turn off in-app purchases" before. I did not know I even needed to know about this. There is no obvious "log out of iTunes" button anywhere either.
The game designer obviously used this flaw as a business model -- no one in their right mind is going to allow their kids to spend hundreds of dollars on crap in a kid's game. The game and others like it is clearly geared toward this kind of inadvertent purchase. At the very least, Apple should disallow in-game purchases by default, and when you turn it on, it should let you know about the 15 minute password thing. It did not. Thankfully, Apple refunded my $200. But it shouldn't have happened in the first place. Every experience I had with the IPad up until that point was that a password was necessary for purchases.
This is kind-of like the old "900" numbers. Any business owner knew to put a "900 block" on a phone that employees had access to. So the crooked companies schemed with the phone company to create a workaround -- call an "800" (free) number and say "I agree to the charges" and the service gets billed to the phone number, and the phone company says "pay the bill or we'll shut you off, but sorry, we have no control over the charges, we're just the billing agent". Someone is always looking to scam you in ways you don't expect.