Discover Series Books for Babies & Toddlers Choo Choo! All aboard! It's time to take a ride with the Discover Series Express! The picture book features full-color photographic illustrations of trains, train tracks, train signs and other things related to the railroad. Used as a jumpstart for interaction, Discover Series Picture Books are a great way to introduce new images, words and concepts to babies and toddlers. Use this photo dictionary as a learning tool. Each photo has a clear title beneath it for identification. Language learners, children, and people looking to build their vocabulary can use this simple book to learn new words.