There are bad developers will not pay your money back and keep their 5 bucks and only refund after a long, long process. They feed on this behavior, for each customer do not challenge those purchases they make free money.

When all the payments are forced to go through a trusted processor with correct parental controls for all apps in the platform, you guarantee that your kid will not make any uninformed purchases.

The thing about fraud is, if you do not stop it completely, it grows exponentially.