These thematic pictures of Thiên nhiên are analogous to a visual dictionary. The theme "Thiên nhiên" 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 vietnamese language, which is not your native language.
To expand your vietnamese language vocabulary on the "Thiên nhiên" topic, flashcards games are the best way: