Donald Crews's Caldecott Honor book Freight Train, beloved by train-crazed toddlers for decades, will win even more fans with the new app available from HarperCollins/Curious Puppy (December 2010).

With the app's interactive elements, even kids who can recite the book backwards and forwards will find surprises. As each component of the train, from red caboose to black engine, is introduced, it latches onto the car before with a satisfying clunk. Exploring the many-hued cars uncovers windows and doors that slide open to reveal staff and stock, freight that can be unloaded and reloaded, billowing smoke and pouring water. Once the train is ready to go, it whizzes past cityscapes and countryside, through tunnels, and out of sight to the strains of a randomly-selected train-themed folk song like "She'll Be Comin' 'Round the Mountain" or "I've Been Working on the Railroad."

The simple, logical presentation of concepts that makes Freight Train so enduring works just as brilliantly here — with the added bonus of ringing bells and blowing whistles.

Like the book, the app is also available in a Spanish-language version, Tren de carga.

Available for iPhone, iPad, and iPod touch (requires iOS 3.1 or later); $0.99. Recommended for preschool users.