These thematic pictures of रंग और आकार are analogous to a visual dictionary. The theme "रंग और आकार" is split 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 that the information is absorbed better. This is especially true if you are using flashcards to learn devanagari language that is not your native language.
To expand your devanagari language vocabulary on the "रंग और आकार" topic, flashcards games are the best way: