"I leave in the morning with the boy and I return with the girl."
Translation:Imím ar maidin leis an mbuachaill agus fillim leis an gcailín.
It’s not a stupid question; it’s never stupid to seek an answer to a question.
You seem to have understood the sentence’s syntax perfectly well; ar maidin is indeed a time descriptor, and given the lack of a pronomial direct object in its independent clause, should be placed at the end of its clause. Report this as an error when opportunity allows for you.
I think that they, like I, went to school back when grammar was taught. The transition occurred later some places then other. On the other hand, I didn't REALLY learn English grammar until I studied another language (Spanish in my case). I do love the distinction between transitive and intransitive verbs which seems to be maintained in Irish, though not in English, where "Enjoy!", originally a transitive verb was adopted for intransitive use--originally by the restaurant industry, I suspect.