Here's why:
* Adjectives describe nouns. In this sentence, "stand" describes the action that Hansel and Gretel are supposed to do.
* "Stand" functions as a verb in the sentence. However, in this case, it's used as a predicate adjective because it modifies the implied noun "they" (which is the implied subject of the infinitive phrase "to stand").
Let me know if you have any other sentences you'd like to analyze!