Timbuktu is an iPad magazine meant for children, and as our friends over at TechCrunch have noted, its developers recently rethought how it implements in-app purchases. The previous incarnation of Timbuktu (and most famously, Smurf Village, among others), made in-app purchases too tempting and easy for children. The result high rates of in-app purchases, which was good for the company but bad for parents who didn't approve of the large associated costs.
Before, Timbuktu had little virtual bubbles that you "popped" to make an in-app purchase. The interface was clearly designed to pique childrens' interest, perhaps too much so. Now, Timbuktu has implemented a subscription plan, so that parents can buy lots of content all at once, and then kids can be free to discover it themselves without accidentally spending any money they're not supposed to.
That definitely sounds more reasonable. It's worth noting that there are other ways to block in-app purchases. For example, Apple's Restrictions settings lets you to disable all in-app purchases entirely. Also, you can customize the amount of time iOS will require your Apple ID between successful App Store purchases. By default it's set to 15 minutes.
Keeping your children from spending too much on in-app purchases is an avoidable problem, and it's good to hear companies like the makers of Timbuktu are taking steps as well.