Currently, Freemium apps account for 65 out of the Top 100 grossing games in the U.S. App Store. App developers are most interested in developing for iOS. Comic apps are also making a charge with the freemium pricing model. 72% of the revenue comes from Apps featuring in-app purchases while only 4% of total iPhone apps include an in-app purchase option.
You may want to block in-app purchases on your iPad if you have little kids using it a lot.