SwipeBeastie is an iPhone/iPad app designed for children. It provides an easy way to create or choose a picture which is hidden behind an overlay. You can then erase the overlay with your finger. This app is not a game, it is a very simple, single purpose application.
Options are to choose an image from the photo library, have the app choose an image at random, or snap a photo of something new. Shake the device, and the overlay resets.