Learn Farsi: کاش بچه‌ها عاقلانه رفتار کرده بودن.

To express an unrealized wish in the past, Farsi uses کاش (kâsh) plus the Past Perfect tense. The verb here is رفتار کرده بودن (raftâr karde budan). It is made by taking the past participle of رفتار کردن (raftâr kardan, meaning to behave or act), which is رفتار کرده (raftâr karde), and adding the simple past of "to be" for the "they" form: بودن (budan).

Why does the verb end in بودن (budan) instead of بودند (budand)?

This sentence is written in a conversational, spoken style. In everyday spoken Farsi, the third-person plural ending often drops the final "d" sound. So, the formal written بودند (budand) simply becomes بودن (budan). You will hear this constantly in natural conversations.

How does the word عاقلانه ('âqelâne) get its meaning of "wisely"?

It is built from the adjective عاقل ('âqel), meaning wise or sensible. By adding the suffix ـانه (-âne) to an adjective, Farsi turns it into an adverb of manner that describes how an action was done. Therefore, it translates to "wisely" or "sensibly."

Does کاش (kâsh) need a pronoun like "I" to mean "I wish"?

No, کاش (kâsh) or its slightly longer form ای کاش (ey kâsh) works entirely on its own to mean "I wish" or "if only." You do not conjugate it or add a subject pronoun to it; it simply sits at the start of the sentence to set a mood of desire or regret.