"I always visit my parents."
Translation:Yo siempre visito a mis padres.
You have to use the personal a for certain types of verbs. I'm no grammar expert but I think it is with transitive verbs, so if the verb directly acts on the person, you use the 'a'. But verbs like tener, you don't. So you wouldn't say tengo a un padre, just tengo un padre.
visitar is the infinitive form of the verb. If you are saying "I visit my parents" the sentence is "Yo visito mis padres." But if you're saying "I want to visit my parents" then the sentence is "Yo quiero visitar mis padres." The direct verb is quiero, and the verb visitar is in infinitive form because it is something like the indirect verb. I believe that's the name of the form. At any rate, that's when you would use the infinitive form. I don't think it's ever correct to say "Yo visitar mis padres."
I think the term you're looking for is "infinitive." Visitar = the infinitive form.
I hope when you see this you can press "edit" and include the "personal a" in your examples, and, to make them even more correct, change them to "mis padres" plural. (a mis padres)
These small but important changes will make your explanation helpful for future readers.
I was marked incorrect because I put "a mi padres" thinking "yo" is singular but I guess it is "mis" because of "padres"?