Old MacDonald (by Duck Duck Moose, the makers of Wheels on the Bus) is an interactive storybook for preschoolers based on the time-honored song of the same name. Kids navigate forward and back through the book's 12 "pages" using touch-screen arrows, and every page offers multiple opportunities for interaction with a simple slide or "poke." The song plays in several languages (English, French, Spanish, Italian, and German) or with just instrumental accompaniment (piano, cello, violin, or kazoo)--or best of all, with a do-it-yourself recorded sing-along, which the app walks you through using karaoke-style subtitles.
The quality of the sound, visuals, and interface is gratifyingly high for a kids' app, with a good mix of straightforward interactivity (poking a farmer to make him dance, or a chicken to make it jump and cluck) and more subtle, complex actions (such as a dumptruck pouring out dirt for a bulldozer to then haul away). As often happens with live renditions of this song, the subject matter can stray far from the "farm"--from a voracious sandwich-eating chihuahua to a three-eyed alien in a rocket--but the interactivity is always clever and fun (and, often, even funny for a grown-ups, such as a Moo Yorker-reading cow).
With its high production values and thoughtful design, Old MacDonald (not to be confused with a dissimilar app of the same name) is one of the better apps available for kids in this age group.