These thematic pictures of Farben und Formen are analogous to a visual dictionary. The theme "Farben und Formen" splits into several parts. For children, especially toddlers from 1 to 5 years old, it is better to divide the sets of cards over several days, or even weeks, so the information is absorbed better. Especially it is true if you are using flashcards to learn the german language, which is not your native language.
To expand your german language vocabulary on the "Farben und Formen" topic, flashcards games are the best way: