"They introduce me to their parents."
Translation:Eles me apresentam a seus pais.
yes, there are some verbs that needs the preposition, we call it indirect transitive verb. Well, Apresentar is a indirect transitive verb, so you have to write the preposition and the article. "aos" - preposition " a " plus the article "os". That's why you can write like this: eles me apresentam a seus pais or eles me apresentam para seus pais.