Some people have had bills in the thousands, which can easily happen even if you are watching a child like a hawk.
Yeh, and its easy to think that a Hawk is a good role model for parents who don't want their kids to buy too many IAPs. But turns out Hawks know pretty much nothing at all about IT and will just perch around on the back of the sofa all day while your kids spend all your money on stupid dragon eggs, or hay, or diamonds, or whatever.
Now if you want to make sure your kids are not eating mice, a Hawk type approach could be fantastic.