Questions & Answers about Дети часто ломают вещи.
Since the current lesson is about short-form past passive participles, how would we say 'The things are broken' to match the lesson's theme?
You would use the short-form past passive participle of the perfective verb сломать (to break). Since вещи is plural, the participle takes the plural ending -ы, giving us Вещи сломаны (The things are broken). Our current sentence uses the active voice (ломают), which is much more common for expressing who is currently doing an action.
Why do we use the imperfective verb ломают here instead of its perfective counterpart?
The adverb часто (often) tells us this is a repeated, habitual action. In Russian, repeated actions always take the imperfective aspect. If you used the perfective form сломают, it would change the meaning to a one-time completed action in the future: 'they will break'.
What case is вещи (things) here? It looks exactly like the nominative plural.
It is in the accusative case because it is the direct object receiving the action of the verb (they break what? -> things). Because вещь is an inanimate noun, its plural accusative form (вещи) is identical to its plural nominative form.
Дети (children) is an irregular plural. What is the singular form of this word?
The singular is ребёнок (a child). This is a completely irregular pair where the plural stem (дет-) is entirely different from the singular stem (ребёнк-). It is a good reminder that not all Russian plurals are formed by simply changing the ending.