Questions & Answers about Дети прячутся за шкафом.
Why is the word шкаф in the instrumental case (шкафом) here?
In Russian, the preposition за takes the instrumental case when it means "behind" and describes a static location (answering the question "where?"). Since the children are already located behind the wardrobe, we use the masculine instrumental ending -ом.
Would it be wrong to say Дети прячут за шкафом without the -ся at the end of the verb?
The dictionary form of the verb is прятаться. Why does the т change to a ч in прячутся?
This is a common consonant mutation in Russian verbs. For many verbs ending in -тать, the т changes to ч throughout the present tense. Also, because of the spelling rule that says we can never write ю after ч, the "they" ending becomes -ут(ся) instead of -ют(ся).
What if the children were running to get behind the wardrobe right now? Would the ending of шкафом change?